Close relationship between diameters at 30cm height and at breast height (DBH)

This paper proposes the establishment of a second diameter measuring standard at 30cm shoot extension ('diam30') as input variable for allometric biomass estimation of small and mid-sized plant shoots. This diameter standard is better suited than the diameter at breast height (DBH, i.e. diameter at 1.30m shoot extension) for adequate characterization of plant dimensions in low bushy vegetation or in primary forest undergrowth. The relationships between both diameter standards are established based on a dataset of 8645 tree, liana and palm shoots in secondary and primary forests of central Amazonia (ranging from 1-150mm dbh). Dbh can be predicted from the diam(30) with high precision, the error introduced by diameter transformation is only 2-3% for trees and palms, and 5% for lianas. This is well acceptable for most field study purposes. Relationships deviate slightly from linearity and differ between growth forms. Relationships were markedly similar for different vegetation types (low secondary regrowth vs. primary forests), soils, and selected genera or species. This points to a general validity and applicability of diameter transformations for other field studies. This study provides researchers with a tool for the allometric estimation of biomass in low or structurally heterogeneous vegetation. Rather than applying a uniform diameter standard, the measuring position which best represents the respective plant can be decided on shoot-by-shoot. Plant diameters measured at 30cm height can be transformed to dbh for subsequent allometric biomass estimation. We recommend the use of these diameter transformations only for plants extending well beyond the theoretical minimum shoot length (i.e., >2m height). This study also prepares the ground for the comparability and compatability of future allometric equations specifically developed for small- to mid-sized vegetation components (i.e., bushes, undergrowth) which are based on the diam(30) measuring standard.

Social wasps of two wetland ecosystems in brazilian Amazonia (Hymenoptera, Vespidae, Polistinae)

In Brazilian Amazonia, 20 genera and more than 200 species of polistine wasps are recorded. Local faunas with 70 to 80 species are usually found in non floodable forest environments. However, a variety of wetlands exist in the region, the most expressive in surface area being varzea systems. In this paper, information is presented on polistines from two areas of wetlands in the Brazilian states of Amazonas and Amapá. These are reciprocally compared and also with nearby terra firme locations. Collecting methods consisted of active search for nests, handnetting and automatic trapping of individuals. Forty-six species of 15 genera were collected in Mamirauá, AM, most being widespread common wasps. However, five species deserve special mention in virtue of rarity and/or restricted distribution: Metapolybia rufata, Chartergellus nigerrimus, Chartergellus punctatior, Clypearia duckei, and Clypearia weyrauchi. In Região dos Lagos, AP, 31 species of 9 genera were collected, nearly all being common species with the exception of some Polistes, like P. goeldi and P. occipitalis. Even though less rich than vespid faunas from terra firme habitats, the Mamirauá fauna proved to be quite expressive considering limitations imposed by the hydrological regime. In Região dos Lagos, however, the very low diversity found was below the worst expectations. The virtual absence of otherwise common species in environments like tidal varzea forests along Araguari River is truly remarkable. The causes of low diversity are probably related to isolation and relative immaturity of the region, allied to strong degradation of forested habitats.

In vitro screening of Amazonian plants for hemolytic activity and inhibition of platelet aggregation in human blood

In the present study, different aerial parts from twelve Amazonian plant species found in the National Institute for Amazon Research's (INPA's) Adolpho Ducke Forest Reserve (in Manaus, Amazonas, Brazil) were collected. Separate portions of dried, ground plant materials were extracted with water (by infusion), methanol and chloroform (by continuous liquid-solid extraction) and solvents were removed first by rotary evaporation, and finally by freeze-drying which yielded a total of seventy-one freeze-dried extracts for evaluation. These extracts were evaluated initially at concentrations of 500 and 100 µg/mL for in vitro hemolytic activity and in vitro inhibition of platelet aggregation in human blood, respectively. Sixteen extracts (23 % of all extracts tested, 42 % of all plant species), representing the following plants: Chaunochiton kappleri (Olacaceae), Diclinanona calycina (Annonaceae), Paypayrola grandiflora (Violaceae), Pleurisanthes parviflora (Icacinaceae), Sarcaulus brasiliensis (Sapotaceae), exhibited significant inhibitory activity towards human platelet aggregation. A group of extracts with antiplatelet aggregation activity having no in vitro hemolytic activity has therefore been identified. Three extracts (4 %), all derived from Elaeoluma nuda (Sapotaceae), exhibited hemolytic activity. None of the plant species in this study has known use in traditional medicine. So, these data serve as a baseline or minimum of antiplatelet and hemolytic activities (and potential usefulness) of non-medicinal plants from the Amazon forest. Finally, in general, these are the first data on hemolytic and inhibitory activity on platelet aggregation for the genera which these plant species represent.

Ethnoveterinary knowledge of the inhabitants of Marajó Island, Eastern Amazonia, Brazil

There have been ethnoveterinary reports from around the world investigating plant usage in therapeutic protocols; however, there is no information regarding the ethnoveterinary practices in Brazilian Amazonia. The objective of this work was to register and document the ethnoveterinary knowledge of the inhabitants of the Island of Marajó, eastern Amazonia, Brazil. In the study, interviews were conducted with 50 individuals, with the application of semi-structured questionnaires that were quantitatively analyzed using descriptive statistic methods of frequency distribution. Use-value was calculated to determine the most important species. Samples of plants that were reported to have medicinal value were collected and identified by botanical classification. Fifty plants, distributed among 48 genera and 34 families, were indicated for 21 different medicinal uses. The family Asteraceae had the largest number of reported species; Carapa guianensis Aubl., Copaifera martii Hayne, Crescentia cujete L., Caesalpinia ferrea Mart., Chenopodium ambrosioides L., Jatropha curcas L. and Momordica charantia L. were species with highest use- value. The plant parts that were more commonly utilized for the preparation of ethnoveterinary medicines were the leaves (56%), bark (18%), roots (14%), seeds (14%) and fruit (8%). With regard to usage, tea was reported as a usage method by 56% of the informants; most preparations (90.9%) utilized only a single plant. In addition to medicinal plants, informants reported using products of animal and mineral origin. The present study contributed to the construction of an inventory of Marajó Island's ethnoveterinary plants, which might be the basis for future scientific validation studies.

Cholini (Coleoptera: Curculionidae: Molytinae) housed in the Invertebrate Collection of the Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil

In Brazilian Amazonia, Cholini (Coleoptera, Curculionidae, Molytinae) is represented by 53 species distributed in seven genera: Ameris Dejean, 1821; Cholus Germar, 1824; Homalinotus Sahlberg, 1823; Lobaspis Chevrolat, 1881; Odontoderes Sahlberg, 1823; Ozopherus Pascoe, 1872 and Rhinastus Schoenherr, 1825. This work documents the species of Cholini housed in the Invertebrate Collection of the Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil and gives the geographical and biological data associated with them. A total of 186 Cholini specimens were identified as belonging to 14 species (13 from Brazilian Amazonia) and five genera (Cholus, Homalinotus, Odontoderes, Ozopherus and Rhinastus). Only 24% of the Cholini species reported from Brazilian Amazonia are actually represented in the INPA collection, underscoring the need for a more systematical collecting based on available biological information. The known geographical distribution was expanded for the following species: Cholus granifer (Chevrolat, 1881) for Brazil; C. pantherinus (Olivier, 1790) for Manaus (Amazonas); Cholus parallelogrammus (Germar, 1824) for Piraquara (Paraná); Homalinotus depressus (Linnaeus, 1758) for lago Janauacá (Amazonas) and rio Tocantins (Pará); H. humeralis (Gyllenhal, 1836) for Novo Airão, Coari (Amazonas) and Porto Velho (Rondônia); H. nodipennis (Chevrolat, 1878) for Carauari, Lábrea (Amazonas) and Ariquemes (Rondônia); H. validus (Olivier, 1790) for rio Araguaia (Brasil), Manaus (Amazonas), rio Tocantins (Pará), Porto Velho and BR 364, Km 130 (Rondônia); Odontoderes carinatus (Guérin-Méneville, 1844) for Manaus (Amazonas); O. spinicollis (Boheman, 1836) for rio Uraricoera (Roraima); and Ozopherus muricatus Pascoe, 1872 for lago Janauacá (Amazonas). Homalinotus humeralis is reported for the first time from "urucuri" palm, Attalea phalerata Mart. ex Spreng.

Tree communities of white-sand and terra-firme forests of the upper Rio Negro

The high tree diversity and vast extent of Amazonian forests challenge our understanding of how tree species abundance and composition varies across this region. Information about these parameters, usually obtained from tree inventories plots, is essential for revealing patterns of tree diversity. Numerous tree inventories plots have been established in Amazonia, yet, tree species composition and diversity of white-sand and terra-firme forests of the upper Rio Negro still remain poorly understood. Here, we present data from eight new one-hectare tree inventories plots established in the upper Rio Negro; four of which were located in white-sand forests and four in terra-firme forests. Overall, we registered 4703 trees > 10 cm of diameter at breast height. These trees belong to 49 families, 215 genera, and 603 species. We found that tree communities of terra-firme and white-sand forests in the upper Rio Negro significantly differ from each other in their species composition. Tree communities of white-sand forests show a higher floristic similarity and lower diversity than those of terra-firme forests. We argue that mechanisms driving differences between tree communities of white-sand and terra-firme forests are related to habitat size, which ultimately influences large-scale and long-term evolutionary processes.

Myxomycetes collection preserved in the herbarium of the Federal University of Roraima (Brazil)

First records of myxomycetes in the North region of Brazil go back to the 19th century. Nevertheless, the myxobiota of this region is still largely unexplored, with only 42 species recorded, distributed in 20 genera and seven families. The objectives of this paper were to characterize the Myxomycetes collection of the Herbarium of the Federal University of Roraima (UFRR) and to add new records for the myxobiota of this State. The collection holds specimens collected in fragments of Open Ombrophilous Forest, Seasonal Semi-deciduous Forest, Riparian Forest, deforested areas and urban home gardens in the state of Roraima. The 157 exsiccates were analyzed and identified or redetermined based on identification keys, descriptions and illustrations. The collection is in good conditions of preservation and includes all subclasses of Myxomycetes, 83% of its orders, 50% of its families, and 20 species. Trichiales, with one family, three genera and six species, represents 62% of all exsiccates. Cribraria aff. splendens, Metatrichia vesparia, Physarella oblonga, Stemonaria longa and Stemonitis splendens are new records for Roraima and Arcyria obvelata, Comatricha pulchella, Stemonitis pallida and Stemonitopsis aequalis are referred for the first time in the Northern Region, enlarging the knowledge of the Brazilian geographic distribution of these species.

Importance of anatomical leaf features for characterization of three species of Mapania (Mapanioideae, Cyperaceae) from the Amazon Forest, Brazil

Mapania belongs to Mapanioideae, a quite controversial subfamily in Cyperaceae due to the existence of unusual characters in both reproductive and vegetative organs. The genus is represented by seven species in Northern Brazil but taxonomic valuable information related to the leaf organs is still unknown. The present study aimed the anatomical description of the leaf organs (either basal leaves or cataphylls and involucral bracts) of three representative Brazilian species of Mapania. Samples of cataphylls, basal leaves and involucral bracts were sectioned and stained for observations under light microscopy. The involucral bracts provide the most elucidative characters (ten) to distinguish the three species The basal leaves provides six distinguishing characters and are useful to M. macrophylla and M. pycnostachya, as they are absent in M. sylvatica. Mesophyll arrangement in the involucral bracts supports the circumscription of M. macrophylla and M. pycnostachya in M. sect. Pycnocephala and of M. sylvatica in M. sect. Mapania. Some features as thin-walled epidermal cells, stomata level and aerenchyma were considered to be adaptive to the humid environment in which the species occur. The translucent cells are here considered as aerenchyma precursors and a supportive function is assumed for the bulliform cells on the basal leaves and involucral bracts. No silica bodies were found which confirm it as a diagnostic character of Mapania among Hypolytreae genera.

Comparative leaf morphological analysis of 20 species of Chrysobalanaceae

Morphological studies focusing on vegetative traits are useful in identifying species when fertile material is not available. The aim of this study was to assess the application of comparative leaf morphology to identify species of the Chrysobalanaceae family. The morphological observations were made with a stereomicroscope. We used the diaphanization technique for viewing venation details. It is shown the descriptions of the leaf morphology, illustrations and an identification key for 20 species from genera Couepia, Licania and Parinari (Chrysobalanaceae) occurring in the Adolpho Ducke Forest Reserve, Manaus, AM, Brazil. The key was constructed using the DELTA (DEscription Language for TAxonomy) software. Leaf traits such as the presence of intersecondary venation and the type of insertion of secondary veins were recorded for each species. These morphological leaf traits are reliable for identifying species of Chrysobalanaceae

Use of anatomical root markers for species identification in Catasetum (Orchidaceae) at the Portal da Amazônia region, MT, Brazil

Orchidaceae is one of the largest botanical families, with approximately 780 genera. Among the genera of this family, Catasetum currently comprises 166 species. The aim of this study was to characterize the root anatomy of eight Catasetum species, verifying adaptations related to epiphytic habit and looking for features that could contribute to the vegetative identification of such species. The species studied were collected at the Portal da Amazônia region, Mato Grosso state, Brazil. The roots were fixed in FAA 50, cut freehand, and stained with astra blue/fuchsin. Illustrations were obtained with a digital camera mounted on a photomicroscope. The roots of examined species shared most of the anatomical characteristics observed in other species of the Catasetum genus, and many of them have adaptations to the epiphytic habit, such as presence of secondary thickening in the velamen cell walls, exodermis, cortex, and medulla. Some specific features were recognized as having taxonomic application, such as composition of the thickening of velamen cell walls, ornamentation of absorbent root-hair walls, presence of tilosomes, composition and thickening of the cortical cell walls, presence of mycorrhizae, endodermal cell wall thickening, the number of protoxylem poles, and composition and thickening of the central area of the vascular cylinder. These traits are important anatomical markers to separate the species within the genus and to generate a dichotomous identification key for Catasetum. Thus, providing a useful tool for taxonomists of this group

Two practical approaches to monitoring the zooplanktonic community at Lago Grande do Curuai, Pará, Brazil

The use of substitute groups in biomonitoring programs has been proposed to minimize the high financial costs and time for samples processing. The objectives of this study were to evaluate the correlation between (i) the spatial distribution among the major zooplankton groups (cladocerans, copepods, rotifers, and testaceans protozoa), (ii) the data of density and presence/absence of species, and (iii) the data of species, genera, and families from samples collected in the Lago Grande do Curuai, Pará, Brazil. A total of 55 sample of the zooplanktonic community was collected, with 28 samples obtained in March and 27 in September, 2013. The agreement between the different sets of data was assessed using Mantel and Procrustes tests. Our results indicated high correlations between genus level and species level and high correlations between presence/absence of species and abundance, regardless of the seasonal period. These results suggest that zooplankton community could be incorporated in a long-term monitoring program at relatively low financial and time costs.

Composition and structure of the fig wasp community in Amazonia

An understanding of the complex ecological interaction between fig wasps and their host plants in Amazonia requires previous knowledge of their distribution and diversity. The objective of this study was to describe the composition and structure of the wasp community associated with four species of Ficus in the municipal area of Manaus, Amazonas, Brazil. A total of 600 syconia from four species were collected. The study species were: Ficus obtusifolia Kunth; Ficus citrifolia Mill; F. americana subspecies guianensis Desv. form mathewsii; and F. americana subspecies guianensis Desv. form parkeriana. Statistical analyses were used to examine the relationship between fig wasp diversity and syconium diameter, and the effect of non-pollinating wasps on numbers of pollinators and seeds. Forty three species of fig wasp were identified, distributed across seven genera (Pegoscapus, Idarnes, Aepocerus, Physothorax, Anidarnes, Heterandrium , Eurytoma). Idarnes (carme group) was the wasps genus non-pollinator with greatest number of individuals with the greatest number of infested syconia (7409 wasps in 376 syconia). Analysing non-pollinating wasp diversity in relation to fig diameter, a significant difference was observed between the four fig species. Ficus citrifolia and F. americana subspecies guianensis form mathewsii had the smallest diameter but the greatest diversity of fig wasp. Ficus obtusifolia was the only species in which the non-pollinating wasps had a significant negative effect on the number of Pegoscapus sp. and on seed production.

Diversity and capacity to promote maize growth of bacteria isolated from the Amazon region

ABSTRACT Maize plants can establish beneficial associations with plant growth-promoting bacteria. However, few studies have been conducted on the characterization and inoculation of these bacteria in the Amazon region. This study aimed to characterize endophytic bacteria isolated from maize in the Amazon region and to assess their capacity to promote plant growth. Fifty-five bacterial isolates were obtained from maize grown in two types of ecosystems, i.e., a cerrado (savanna) and a forest area. The isolates were characterized by the presence of the nifH gene, their ability to synthesize indole-3-acetic acid (IAA) and solubilize calcium phosphate (CaHPO4), and 16S rRNA partial gene sequencing. Twenty-four bacteria contained the nifH gene, of which seven were isolated from maize plants cultivated in a cerrado area and seventeen from a forest area. Fourteen samples showed the capacity to synthesize IAA and only four solubilized calcium phosphate. The following genera were found among these isolates: Pseudomonas; Acinetobacter; Enterobacter; Pantoea; Burkholderia and Bacillus. In addition, eight isolates with plant growth-promoting capacity were selected for a glasshouse experiment involving the inoculation of two maize genotypes (a hybrid and a variety) grown in pots containing soil. Inoculation promoted the development of the maize plants but no significant interaction between maize cultivar and bacterial inoculation was found. A high diversity of endophytic bacteria is present in the Amazon region and these bacteria have potential to promote the development of maize plants.

Morphology, ontogeny and structure of the stipular nectaries in Caamembeca spectabilis (Polygalaceae)

ABSTRACT Nodal glands are found in one third of the Polygalaceae genera and have valuable taxonomic, ecological and evolutionary significance. In Brazil, they occur in five of the eleven genera already registered. However, there is still a controversy regarding the origin of these structures. The objective of this study was to characterize the morphology and the origin of nodal glands inCaamembeca spectabilis, in order to increase the structural and functional knowledge of these glands in the genera. Samples of nodal regions were collected, fixed and processed according to the methods of light microscopy and electron scanning. Ants were observed and identified along the stem axis. The glucose in exudate allows us to classify these glands as extrafloral nectaries. They are located in pairs on the nodal region. However, its origin is in the leaf trace. In the longitudinal section, the nectaries were present in the apex of cells with anticlinal walls impregnated with suberin, which represents the first record for the family. In this region there is also the formation of a hole by lysis. The secretory tissue is surrounded by phloem. Xylem vessels were observed only on the basis of the nectary, where there are also idioblasts with crystals in druse type. We have studied the ontogeny of the glands nodal in Caamembeca spectabilis and unveiled that these glands are linked to the leaves as stipular nectaries. In addition, the new findings presented here may add support for the understanding of morphology and anatomy of nodal glands in Caamembeca.

Estudos experimentais sôbre a origem do milho

1) It may seem rather strange that, in spite of the efforts of a considerable number of scientists, the problem of the origin of indian corn or maize still has remained an open question. There are no fossil remains or archaeological relics except those which are quite identical with types still existing. (Fig. 1). The main difficulty in finding the wild ancestor- which may still exist - results from the fact that it has been somewhat difficult to decide what it should be like and also where to look for it. 2) There is no need to discuss the literature since an excellent review has recently been published by MANGELSDORF and REEVES (1939). It may be sufficient to state that there are basically two hypotheses, that of ST. HILAIRE (1829) who considered Brazilian pod corn as the nearest relative of wild corn still existing, and that of ASCHERSON (1875) who considered Euchlaena from Central America as the wild ancestor of corn. Later hypotheses represent or variants of these two hypotheses or of other concepts, howewer generally with neither disproving their predecessors nor showing why the new hypotheses were better than the older ones. Since nearly all possible combinations of ideas have thus been put forward, it har- dly seems possible to find something theoretically new, while it is essential first to produce new facts. 3) The studies about the origin of maize received a new impulse from MANGELSDORF and REEVES'S experimental work on both Zea-Tripsacum and Zea-Euchlaena hybrids. Independently I started experiments in 1937 with the hope that new results might be obtained when using South American material. Having lost priority in some respects I decided to withold publication untill now, when I can put forward more concise ideas about the origin of maize, based on a new experimental reconstruction of the "wild type". 4) The two main aspects of MANGELSDORF and REEVES hypothesis are discussed. We agree with the authors that ST. HILAIRE's theory is probably correct in so far as the tunicata gene is a wild type relic gene, but cannot accept the reconstruction of wild corn as a homozygous pod corn with a hermaphroditic tassel. As shown experimentally (Fig. 2-3) these tassels have their central spike transformed into a terminal, many rowed ear with a flexible rachis, while possessing at the same time the lateral ear. Thus no explanation is given of the origin of the corn ear, which is the main feature of cultivated corn (BRIEGER, 1943). The second part of the hypothesis referring to the origin of Euchlaena from corn, inverting thus ASCHERSON's theory, cannot be accepted for several reasons, stated in some detail. The data at hand justify only the conclusion that both genera, Euchlaena and Zea, are related, and there is as little proof for considering the former as ancestor of the latter as there is for the new inverse theory. 5) The analysis of indigenous corn, which will be published in detail by BRIEGER and CUTLER, showed several very primitive characters, but no type was found which was in all characters sufficiently primitive. A genetical analysis of Paulista Pod Corn showed that it contains the same gene as other tunicates, in the IV chromosome, the segregation being complicated by a new gametophyte factor Ga3. The full results of this analysis shall be published elsewhere. (BRIEGER). Selection experiments with Paulista Pod Corn showed that no approximation to a wild ancestor may be obtained when limiting the studies to pure corn. Thus it seemed necessary to substitute "domesticated" by "wild type" modifiers, and the only means for achieving this substitution are hybridizations with Euchlaena. These hybrids have now been analysed init fourth generation, including backcrosses, and, again, the full data will be published elsewhere, by BRIEGER and ADDISON. In one present publication three forms obtained will be described only, which represent an approximation to wild type corn. 6) Before entering howewer into detail, some arguments against ST. HILAIRE's theory must be mentioned. The premendelian argument, referring to the instability of this character, is explained by the fact that all fertile pod corn plants are heterozygous for the dominant Tu factor. But the sterility of the homozygous TuTu, which phenotypically cannot be identified, is still unexplained. The most important argument against the acceptance of the Tunicata faetor as wild type relic gene was removed recently by CUTLER (not yet published) who showed that this type has been preserved for centuries by the Bolivian indians as a mystical "medicine". 7) The main botanical requirements for transforming the corn ear into a wild type structure are stated, and alternative solutions given. One series of these characters are found in Tripsacum and Euchlaena : 2 rows on opposite sides of the rachis, protection of the grains by scales, fragility of the rachis. There remains the other alternative : 4 rows, possibly forming double rows of female and male spikelets, protection of kernels by their glumes, separation of grains at their base from the cob which is thin and flexible. 8) Three successive stages in the reconstruction of wild corn, obtained experimentally, are discussed and illustrated, all characterized by the presence of the Tu gene. a) The structure of the Fl hybrids has already been described in 1943. The main features of the Tunicata hybrids (Fig. -8), when compared with non-tunicate hybrids (Fig. 5-6), consist in the absence of scaly protections, the fragility of the rachis and finally the differentiation of the double rows into one male and one female spikelet. As has been pointed out, these characters represent new phenotypic effects of the tunicate factor which do not appear in the presence of pure maize modifiers. b) The next step was observed among the first backcross to teosinte (Fig. 9). As shown in the photography, Fig. 9D, the features are essencially those of the Fl plants, except that the rachis is more teosinte like, with longer internodes, irregular four-row-arrangement and a complete fragility on the nodes. c) In the next generation a completely new type appeared (Fig. 10) which resembles neither corn nor teosinte, mainly in consequence of one character: the rachis is thin and flexible and not fragile, while the grains have an abscission layer at the base, The medium sized, pointed, brownish and hard granis are protected by their well developed corneous glumes. This last form may not yet be the nearest approach to a wild grass, and I shall try in further experiments to introduce other changes such as an increase of fertile flowers per spikelet, the reduction of difference between terminal and lateral inflorescences, etc.. But the nature of the atavistic reversion is alveadwy such that it alters considerably our expectation when looking for a still existing wild ancestor of corn. 9) The next step in our deductions must now consist in an reversion of our question. We must now explain how we may obtain domesticated corn, starting from a hypothetical wild plant, similar to type c. Of the several changes which must have been necessary to attract the attention of the Indians, the following two seem to me the most important: the disappearance of all abscission layers and the reduction of the glumes. This may have been brought about by an accumulation of mutations. But it seems much more probable to assume that some crossing with a tripsacoid grass or even with Tripsacum australe may have been responsible. In such a cross, the two types of abscission layer would be counterbalanced as shown by the Flhybrids of corn, Tripsacum and Euchlaena. Furthermore in later generations a.tu-allele of Tripsacum may become homozygous and substitute the wild tunicate factor of corn. The hypothesis of a hybrid origin of cultivated corn is not completely new, but has been discussed already by HARSHBERGER and COLLINS. Our hypothesis differs from that of MANGELSDORF and REEVES who assume that crosses with Tripsacum are responsible only for some features of Central and North American corn. 10) The following arguments give indirects evidence in support of our hypothesis: a) Several characters have been observed in indigenous corn from the central region of South America, which may be interpreted as "tripsacoid". b) Equally "zeoid" characters seem to be present in Tripsacum australe of central South-America. c) A system of unbalanced factors, combined by the in-tergeneric cross, may be responsible for the sterility of the wild type tunicata factor when homozygous, a result of the action of modifiers, brought in from Tripsacum together with the tuallele. d) The hybrid theory may explain satisfactorily the presence of so many lethals and semilethals, responsible for the phenomenon of inbreeding in cultivated corn. It must be emphasized that corn does not possess any efficient mechanism to prevent crossing and which could explain the accumulation of these mutants during the evolutionary process. Teosinte which'has about the same mechanism of sexual reproduction has not accumulated such genes, nor self-sterile plants in spite of their pronounced preference for crossing. 11) The second most important step in domestication must have consisted in transforming a four rowed ear into an ear with many rows. The fusion theory, recently revived byLANGHAM is rejected. What happened evidently, just as in succulent pXants (Cactus) or in cones os Gymnosperms, is that there has been a change in phyllotaxy and a symmetry of longitudinal rows superimposed on the original spiral arrangement. 12) The geographical distribution of indigenous corn in South America has been discussed. So far, we may distinguish three zones. The most primitive corn appears in the central lowlands of what I call the Central Triangle of South America: east of the Andies, south of the Amazone-Basin, Northwest of a line formed by the rivers São Prancisco-Paraná and including the Paraguay-Basin. The uniformity of the types found in this extremely large zone is astonishing (BRIEGER and CUTLER). To the west, there is the well known Andian region, characterized by a large number of extremely diverse types from small pop corn to large Cuszco, from soft starch to modified sweet corn, from large cylindrical ears to small round ears, etc.. The third region extends along the atlantic coast in the east, from the Caribean Sea to the Argentine, and is characterized by Cateto, an orange hard flint corn. The Andean types must have been obtained very early, and undoubtedly are the result of the intense Inca agriculture. The Cateto type may be obtained easily by crosses, for instance, of "São Paulo Pointed Pop" to some orange soft corn of the central region. The relation of these three South American zones to Central and North America are not discussed, and it seems essential first to study the intermediate region of Ecuador, Colombia and Venezuela. The geograprical distribution of chromosome knobs is rapidly discussed; but it seems that no conclusions can be drawn before a large number of Tripsacum species has been analysed.