342 



MORPHOLOGY OF GYMNOSPERMS 



(figs. 389-391). In Microcachrys (151, 163) the situation in 

 Dacrydium is repeated, three (more frequent) or four prothalUal 

 cells appearing, depending upon the division of one or both of 

 the two primary cells (fig. 393) ; and the prothallial tissue of Saxe- 

 gothaea (149) is exactly ths same (figs. 394, 395). In these three 



genera, the second 

 prothallial cell always 

 divides and the first 

 also may divide, and 

 at pollination three or 

 four free vegetative 

 nuclei are found in the 

 grain. Podocarpus is 

 much more variable 

 (69, 128, 139), the 

 number of prothallial 

 cells and free nuclei 

 varying from one to 

 eight (fig. 396). Only 

 one prothallial cell 

 may be cut off, and it 

 may not divide; but 

 usually there are two 

 primary cells, the sec- 

 ond of which always 

 divides and both of 

 which may, and in 

 both cases there may 

 be still another divi- 

 sion. Therefore, there 

 may be one, three, four, six, or eight prothallial cells, and subse- 

 quently the same number of free vegetative nuclei that swarm into 

 the pollen tube. 



This behavior of the male prothallial tissue among the podocarps 

 is not only constant and striking, but it is the same in kind as that 

 observed among the araucarians (p. 277), the only difference being 

 that the vegetative cells and free nuclei in the latter group reach a 



Fig. 397. — Phyllodadus alpiiia: the two unequal 

 male cells, with the stalk and tube nuclei and one 

 prothallial nucleus in advance; the archegonium shows 

 a four-celled neck and a definite jacket; the egg is ready 

 for fertilization; X440.— After Miss Young (174)- 



