92 



BOTANICAL GAZETTE [seppemijer 



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BidwiUii. A very close series was secured, showing spindles in 



w 



every one of the divisions^ so that the sequence of events was quite 

 clear. In this species, very rarely, a division of the first prothallial 

 cell occurs. In D. cupressinuniy however, this takes place normally, 

 giving a complex of six instead of five cells {jig. ii). As early stages 

 were not secured, I cannot say when the division occurs. 



The next step in the development of the gametophyte is the enlarge- 

 ment of the two generative daughter cells. They increase in thick- 

 ness and the nuclei lose their flattened appearance. Before this 

 there had been nothing by which to distinguish between the two, but 

 now one of them grows more rapidly than the other and arches upward 

 conspicuously. This may take place before or after the division 

 of the second prothallial cell. At the same time the upper and inner 



■ 



walls become gradually less and less distinct and finally disappea 

 altogether (figs. 8, p, lo). The larger cell does not lose its identity, 

 but retains about itself a sheath of cytoplasm, rich in starch. It 

 abandons all connection with the spore wall and appears as a rounded 

 cell free within the pollen grain, similar to the body cell of other 

 conifers. The other loses itself in the general cytoplasm and its 

 nucleus is set free. 



The prothallial cells now also increase somewhat in thickness, 

 their nuclei round up, and their walls fade away. When ready to 

 be shed, the pollen grain of D. BidwiUii contains the body cell and 

 five free nuclei. These change their relative positions somewhat, and 

 the nucleus of the body cell is indistinguishable from those of the 

 prothallial cells and the tube nucleus. 



Several pollen grains of D. BidwiUii were found in which two body 

 cells were apparently developing from the divided generative cell; 

 though these were unequal in size, both had the characteristic sheath. 

 In two or three older pollen grains of D. laxifolium, in which the tubes 

 were formed, there was the appearance of two body cells, one larger 

 than the other; fig, ij shows one of these cases, though not the most 

 pronounced. 



D. laxijoliiim, though collected on the same day with the micro- 

 spores of D. bifoffne and the more advanced D. BidunUii, showed 

 no young stages at all. The pollen had all been shed. The micro- 

 pyles were full of the pollen grains, of which some had not germinated, 



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