2 74 



MORPHOLOGY OF GYMNOSPERMS 



appear merely as two thin and darkly staining disks, which are over- 

 grown rapidly by the intine. These two evanescent cells represent 

 the only vestige of the vegetative tissue of the male gametophyte, and 

 hence are called vegetative (sometimes prothallial) cells. It will 

 be recalled that only one such cell appears among the cycads, and 

 that it persists; while in Ginkgo two appear, the first disorganizing 

 while the second one persists. 



The third (large) cell, which is sister to the second evanescent 

 vegetative cell, is an antheridial cell in the sense that it gives rise to 

 the series of cells that represent the antheridium in function, but 



Fig. 314. — Pinus Strohus: microspore with nucleus in prophase of first division; 

 the broad dotted portion of the wall was described as a third coat; June 7, 1898; 

 X810. — After Miss Ferguson (87). 



not at all in structure. The division of this cell follows immediately, 

 giving rise to the generative cell (cut off against the evanescent vege- 

 tative cells) and the tube cell (the larger portion of the antheridial 

 cell, containing the tube nucleus). This conspicuous tube nucleus 

 was regarded as the generative nucleus until 1891, when Belajeff 

 {2,2)) discovered its true function. The exine and intine are differen- 

 tiated quite early, and both are thickest at the prothallial end of the 

 spore (figs. 305-312). Miss Ferguson (87) described a third coat, 

 but it was evidently only the thicker intine of the basal region of the 

 spore (fig. 314). 



No further division takes place until the following spring, a period 

 of about eleven months, and in this condition pollination occurs. 

 As the pollen is being shed, a drop of mucilaginous substance secreted 

 by the upper part of the nucellus appears at the apex of the ovule, 



