3i8 



GYMNOSPERMS 



that the outer wall of the body cell becomes part of the wall of 

 the sperm cell, does not appear from these figures. At any rate, 

 the sperm lacks only the cilia to make it motile, like the sperms of 

 cycads and Ginkgo. 



Fig. 316. — Pollen tube structures in the Cupressaceae: A, B, Thuja occideniulis: A, 

 body cell, with stalk and tube nuclei; B, the two sperms; XsOo; after Land;'" C, Cii- 

 pressus gowcuiaua; Rroup of numerous male cells, with stalk and tube nuclei below; 

 X3S0; after Ji ix;"" /;, Libocedrus decurrens; the two sperms; after Lawson."' 



In nearly all cases where the sperms are so highly organized, the 

 sperms appear to be exactly alike in size and structure; but in Taxus, 

 Cephalotaxus, and Torrcya, there is great disparity in size. The mi- 



