

284 BOTANICAL GAZETTE [APRIL 
cytology. In material collected about the middle of April, before the snow 
had disappeared, the mother cell of the megaspore is easily distinguished by 
its large size, and by the abundance of starch. The first division is hetero- 
typic, and shows the reduced number (12) of chromosomes. At the poles of 
the spindle are granular masses which may possibly represent centrosomes, 
although the author is not willing to commit himself to this interpretation. 
During the anaphase the starch disappears, a cell wall is formed, and each 
of the two daughter nuclei divides, this time by a homotypic division, giving 
rise to a row of four megaspores, the lowest of which germinates and pro- 
duces the gametophyte. By comparing this series with the development of 
the microspores, which has been thoroughly studied in Larix, the author 
reaches the conclusion that the two series are homologous, and that the 
megaspore, like the microspore, arises by a tetrad division. While the con- 
clusion is not new, the evidence supporting it is valuable. 
Il. Zhe tetrad formation in a hybrid plant — It has long been known that 
hybrids are inclined to be sterile, and that the pollen of hybrid plants is 
commonly imperfect. The present paper deals with the formation of the 
tetrad in Syringa Rothamagensis, a hybrid between S. vulgaris and S. Per- 
sica. The form did not prove to be favorable for such a problem, because 
the pollen of both parents is poor, in S. vudgaris about 50 per cent. of the 
pollen grains appearing to be incapable of functioning, and in S. Perstca 
normal pollen being quite rare. The latter form is almost as sterile as the 
hybrid. In all three forms the development is normal up to the formation of 
the pollen mother cells. In the hybrid it was found that while most of the 
divisions in these cells were mitotic, there were also numerous instances of 
amitotic division, and abnormalities in the chromatin and in the achromatic 
figure were frequent. 
Ill. The development of the pollen grain of Carex.—As a rule, the pollen 
mother cell of a spermatophyte gives rise to four pollen grains, but it has 
been reported that in the Asclepiadaceae and Cyperaceae the mother cell 
gives rise to one pollen grain only. A careful examination of Carex acuta 
showed that the wall of the pollen mother cell becomes the wall of the pollen 
grain. It also showed that the tetrad divisions take place, but the walls are 
imperfect and only one cell of the tetrad develops into a pollen grain, the 
other three being crowded out, just as in the megaspore series three potential 
megaspores are crowded out by the one that functions CHARLES J. CHAM- 
BERLAIN, 

