Microsporogênese em Araucária angustifolia (Bertoloni) O. Ktze.

Resumo

Studying the microsporogenesis of A. angustifolia in Viçosa, State of Minas Gerais, we have obtained some cytological data about the meiosis in this gymnosperm.

In microspore mother cells which are very near the beginning of prophase of the first mitosis the nucleoli have already disappeared. The nuclear membrane disappears during the pachynema stage.

The chromatin has an accentuated tendency to shrink during .the stages that follow the zygonema stage.

Being 4. angustifolia a dioicious plant we thought to find sex chromosomes belonging to the types already described for several plants and animals.

We could not find any difference between the members of a same diad, but we observed to be frequent a physio- logical behavior, different from that of the other chromosomes in the members of a same chromosomic tetrad.

These chromatids begin first the poleward movement as it was observed by Wilson in the Hemipterus Oncopelius fasciatus. By their function in advance and by some slight differences presented by them, they could be differenciated from the others during anaphase.

In Viçosa the reduction division occurs in September. Polen grains begin to be shed in the last days of September.

The pollen grains were found germinated two months after pollination.

The period that goes from pollination to fertilization is about one year and one month.