290 BOTANICAL GAZETTE [apeil 



so-called double gametophyte (figs. R-U and 28, 29, 31, 32); when 

 the first primary derivative is surrounded by cytoplasm it divides, 

 giving rise to a spermatogenous and a sterile cell (figs. K-M and 

 9, 12, 30). In this case there is no further division of the primary 

 cell; the first primary derivative becomes the functioning antherid- 

 ial cell. Again, if the first cell cut off contains sufficient protoplasm 

 it may divide once or even twice to form as many as four free 

 nuclei. When this occurs, the primary cell soon ceases to divide 

 and begins to disintegrate (figs. N-Q and 28, 29, 33). The first 

 primary derivative may function as an antheridial cell by directly 

 dividing to form a spermatogenous and a sterile cell, by repeatedly 

 dividing to form a number of free nuclei, or by becoming primary 

 in nature and hence developing along with its sister cell to form a 

 bi-antheridial gametophyte. 



When the first primary cell is evanescent, a second primary 

 division takes place. Nor is it uniform. Frequently the primary 

 cell approaches the first primary wall before dividing, and it may 

 come into contact with this wall. The second primary derivative 

 is then cut off as a lenticular cell against the wall of the first and 

 soon disintegrates (figs. C-E and 23, 25, 26). If, however, it remains 

 imbedded in the cytoplasm of the primary cell, it divides to form 

 a spermatogenous and a sterile cell (figs. F-I and 25, 38). Hence 

 the second primary derivative may function as an antheridial cell. 



When, as it has been hitherto described, the first and second 

 primary derivatives are evanescent, a third primary division takes 

 place, and the last cell cut off functions as the antheridial cell 

 (figs. A-E and 42-51). 



Since the spermatogenous cell may originate from the first, 

 second, or third primary derivatives, we are forced to the conclusion 

 that these cells are all potentially antheridial, one or in some cases 

 two functioning as such. They may be known as evanescent or 

 functioning antheridial cells, as the case may be. 



Development; time; nutrition 



Growth is exceedingly rapid; in three days the diameter of the 

 pollen grain is doubled, its volume becoming four times as great. 

 In Pinus " the mature pollen grain has the same size and form as 



