CONIFERALES 



93 



the stalk cell and body cell (Fig. 69, L). In this case the two 

 cells, so far as we have observed or seen figured, are " fore 

 and aft " with reference to each other, and not side by side, 

 as in Cycads and Ginkgo, the stalk cell being nearer the old 

 spore wall. It appears, therefore, that the generative cell per- 

 sists for about eleven months without dividing. The pollen 

 tube branches as it traverses the nucellus, not so extensively as 

 do the tubes of Cycads and Ginkgo, but sufficiently to give evi- 

 dence of its primitive service as an absorbing or rhizoidal organ. 

 It consumes about two months in traversing the nucellus after 

 its second start, entering the archegonium about the 1st of July. 



The liberation and descent of the body cell into the tube, 

 accompanied by the freed nucleus of the stalk cell whose wall 

 has been ruptured, and their association with the tube nucleus 

 near the tip of the tube, has been described in detail by Dixon 

 for Pinus silvestris, and his account applies as well to Pinus 

 Laricio, except that we find 

 no definite order of arrange- 

 ment in the relative posi- 

 tions of these three bodies. 



Just before fertilization, 

 about two months after the 

 diA^ision of the generative 

 cell into stalk and body cells, 

 the latter divides and forms 

 the two male cells (mor- 

 phologically sperm mother 

 cells). It is this division 

 which in the Cycads is ac- 

 companied by the appear- 

 ance of blepharoplasts, and 

 results in the organization 



of two ciliated male cells. So far as observed, however, bleph- 

 aroplasts do not appear in Conifers and the male cells do not 

 become ciliated. This is doubtless associated with the fact that 

 in Conifers the pollen tube has become a sperm carrier, while 

 in the Cycads it performs no such function. At the time of fer- 

 tilization, besides dense cytoplasm rich in starch, the tip of the 

 pollen tube contains four bodies, namely, tube nucleus, stalk 

 cell nucleus, and the two male cells (Figs. 70-72). 



FIG. 72. Juniperus Virginiana, showing 

 the ends of two pollen tubes ; in the tube 

 to the left the body cell has not yet di- 

 vided ; in the other the division into two 

 male cells has just taken place ; in both 

 cases the nuclei of the tube and stalk cells 

 are in front; x 160. After STRASBURGER. 



