220 BOTANICAL GAZETTE [march 



persistent one (figs. 10-12) . The illusion is emphasized by the fact 

 that deeply staining granules simulating a broken-down nucleus 

 are sometimes found at the base of the prothallial cell (fig. 15). It 

 seems probable that a misinterpretation of this sort was responsible 

 for the description of an evanescent prothallial cell. 



The nucleus in the main body of the grain now divides again, the 

 mitosis resulting in the formation of a tube cell and a cell which 

 resembles the prothallial cell and becomes so closely applied to it 

 that the two look as if they had arisen by the division of the prothallial 

 cell (figs. 7-0). This cell, so closely associated with the prothallial 

 cell, has been called the generative cell. It soon divides, giving rise 



id body cells (fig. id) . The tube nucleus, even before 



formation 



hich 



is to form the pollen tube becomes filled with large starch grain 

 Late in September the pollen is shed in this three-celled condition. 



The output of spores can be estimated with reasonable accuracy 

 by the formula f7rR3=the number of spores in a sporangium. 

 To apply the formula, it is necessary only to count the number of 

 spores in a line from the center of the sporangium to the tapetum. 

 substitute this number for R, and then make the calculation. Of 

 course, this assumes that the mass of soores is spherical and that all 



assumpt 



Idual 



sporangia of average size. In a few cases, spores were actually 

 counted in a series of sections and the results were practically identical 

 with the estimates by the formula. In the larger sporangia there are 

 about 20 spores in a radius, and consequently the output is about 

 33.507 spores. The largest sporangia, with a radius of 22 spore 

 would have an output of 44,600 spores. In some of the smaller 

 sporangia, which nevertheless produce good spores, the o^P 11 * **; 

 fall as low as 8000 spores. About t,c 



000 



ded 



ium oi Vioon euw 



,i ~iinn is shed 



oozes 



» and consistent *» o - 

 As the pollen passes throug 



the drop into the pollen chamber, at least a portion of the drop becomes 



brownish and so hard that it adds 



