﻿274 BOTANICAL GAZETTE [afril 



division follows the heterotypic or homotypic mitoses, although 

 there is sometimes a tendency toward cell-plate formation (Mot- 

 tier, '98), and these two nuclear divisions represent two out of 

 the three divisions in the embryo-sac. 



In the light of these facts, it seems clear that in Lilium there 

 is merely a shortening of the development of the embryo-sac 

 by two typical mitoses. 



The development of the embryo-sac immediately from the 

 mother-cell has probably no parallel in the case of the pollen, 

 since Strasburger (1901) and Frye (1901) have recently shown 

 that in Asclepias and in a few other genera, in which the pollen 

 mother-cell was supposed to function as the spore, the usual 

 process of the development of the pollen obtains. 



SUMMARY. 



In the karyokinetic processes occuring in the micro- and 

 macrospore mother-cells of the angiosperms, certain phenomena 

 may now be regarded as very well understood and pretty 

 definitely established. 



In the first place, the nuclear spindle arises as a multipolar 

 complex of fibers, wholly or almost wholly of cytoplasmic origin, 

 which is gradually transformed into the typical bipolar spindle. 

 No centrospheres or centrosomes are present. 



During the first mitosis the reduced number of chromosomes 

 appears. There is no reduction or qualitative division in the 

 sense of Weismann. The first division is characterized further 

 by two longitudinal divisions of the chromatin, the second 

 longitudinal splitting being at right angles to the plane of the 

 first. 



The first longitudinal fission occurs in the early prophase; 

 the second is demonstrable in the mature spindle when the 

 chromosomes are arranged in the nuclear plate, or first during 

 the meta- or anaphase. Sometimes evidence of the second 

 splitting appears at an earlier stage, but these are not conclusive. 



The second longitudinal fission seems to be a preparation for 

 the second or following mitosis. 



The first division is also characterized by the long period of 



