CONIFERALES 



319 



totic figure in the body cell is so near the periphery that one of the 

 sperms is only a small lenticular cell which soon aborts (fig. 317). 



The formation of sperms in pairs is thoroughly estabHshed in the 

 liverworts, and probably goes farther back; but, from the liverworts 

 to the sunflowers and orchids the pairing is constant. In the angio- 

 sperms, each sperm has its own function, one 

 fertilizing the egg and the other taking part 

 in the triple fusion which initiates the second 

 period in the development of the female ga- 

 metophyte. In gymnosperms, in many cases, 

 the two sperms differ in size, but whether 

 they differ in chromatin content or in any 

 other way, has not been determined, either 

 in gymnosperms or in any other group. We 

 suspect that a detailed investigation, with 

 adequate technique, would reveal something 

 interesting. 



In Cupressus goweniana, and also in C. ari- 

 zonica, there are several small sperms (fig. 

 316 C). In the latter species Doak'^^ found 

 twelve fully developed sperms. Both of these 

 investigators used exotic material. These 

 two species recall the condition in Micro- 

 cycas, which has a dozen or more sperms. 



It is worth while to note that these highly 

 organized sperms, doubtless primitive, are 

 associated with archegonia in which there is no wall between the 

 ventral canal nucleus and that of the egg, a feature which is more 

 advanced than that in Ginkgo and the Abietaceae, where there is a 

 wall between these two nuclei. It is an instructive illustration of the 

 fact that various lines of evolution do not keep pace with each other. 



In the Abietaceae the sperms are very different. The wall of the 

 body cell is thin, and when its nucleus divides, the daughter-nuclei 

 are left free, with no wall between them. A wall begins to form at 

 the equator of the spindle, but it soon breaks down. The wall of the 

 body cell, although very thin, separates the cytoplasm surrounding 

 the sperm nuclei from the general cytoplasm of the pollen tube, dur- 



FiG. 317. — Taxus cana- 

 densis: A , body cell divid- 

 ing to form two unequal 

 sperms; B, the two sperms; 

 the stalk and body nuclei 

 are shown at the left; 

 X570; after Dupler.''^ 



