Views of several authors concerning the natural regeneration of the cerrado (Brazilian wooded savanna) are summarized. Except for one, all of them agree that seed germination and seedling growth are disturbed by the harsh environmental conditions that prevail in the savanna. Unfavorable factors that have to be taken into account are dryness at soil surface, rather long drought period, and, above all, fire. Vegetative reproduction, on the other hand, is pointed out by the same writers as the most common means of maintenance and spread of the cerrado; the extent to which the plants set offspring vegetatively seems to be closely related to the degree of disturbance wrought in the cerrado environment by the factors mentioned above. For the study reported in this paper, many plants were grown in Rio de Janeiro (rain forest) zone) and at Paraopeba (cerrado zone), and observed from seed germination. A number of mature trees were also kept under observation in a small cerrado stand located in the Botantical Garden of Rio de Janeiro. A large number of data dealing primarily with seedling development is tabulated, with special reference to the length attained by both the primary root and the shoot at various ages. Data are also included which elucidate the germination features. Evidence is presented which indicates that, up to an age of two years, no taproot succeeds in reaching a depth of lm. Thus the plantlets are forced to pass through 1-2 drought periods with their roots in the driest portion of the soil. It is recalled that in dry, sunny stations the cell walls are far more lignified and suberized in shoots and roots, and that the root cap cell walls are endowed with pectin, whose water-retaining ability is well-known. Accordingly, the suggestion is made that the real critical period in the establishment of seedlings in dry places is, as a matter of fact, the very early stages of development, when the cell wall devices have not had time yet to attain the necessary degree of completeness. It is suggested that many woody species peculiar to the cerrados would make their best growth il they received some additional water; this seems to mean that the seedlings would require favorable sites to become established in nature, where human disturbance and drought conditions are reduced to a minimum. However, this point must await fresh data from various sources. It has been verified that a number of seedlings can bear the destruction of either the primary root or the shoot; provided they are sufficiently watered, they soon remake the lost parts. Epigeal germination, which is mostly observed in trees, prevails largely over hypogeal germination; this in turn occurs primarily in undershrubs. A number of stowing tissues from underground tuberized organs were analysed lor their water content; it ranged from 44 to 91% according to the ligneous or fleshly nature of the parts involved. The role of fire as a destructive agent for both seeds and seedlings is emphasized; insect larvae are also mentioned in this connection.
Continuando a apresentação do nosso dicionário para uso dos botânicos, seguem-se as letras compreendidas entre I e M. As notas explicativas, como autores utilizados e abreviaturas, acham-se na “Advertência” da primeira publicação da série, nos Arquivos do Jardim Botânico (cf. Bibliografia).
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