1909] 



CHAMBERLAIN— SPERMATOGENESIS IN DIOON 



231 



That the two sperms represent a reduction from a larger number 

 is so evident that there is no need for discussion, but a word in regard 

 to the so-called "body cell" from which they are produced may not 

 be out of place. In the cycads, in Ginkgo, and in Coniferales the 

 cell whose division gives rise to the "stalk cell" and body cell is 

 often called the generative cell, probably because the stalk cell is 

 regarded as a spermatogenous cell which has ceased to function. 



Microcy 



and Ceratozamia all the sperms 



from the body cell, the stalk cell being entirely sterile. It might be 



F IG. 33.— Diagram illustrating the homologies between the parts of an ordinary 



Polypod fem antheridium and the pollen tube structures of a cycad: A and C, the 



fern antheridium, in C the dome cell being represented as elongated into a tube; B and 



D the cycad structures: p, prothallial cell; s, stalk cell; sp, spermatogenous cell; t, 

 tube cell. 



quinary tern antheridium and that the dome cell corresponds 10 wc 

 Pollen tube, while the primary spermatogenous cell corresponds to the 

 kty cell. If the dome cell, without forming the usual cover cell, 

 should become elongated, we should have very much the same situa- 



Cupressus Goweniam, Microcy cas 



ozamia mexicana. The 



the 



cana. The diagram (fig. 



rdinary polypod fern and a 

 le lern tn e dome cell is sister to the sperma 

 cycad the stalk and spermatogenous cells 



indicates these 

 The fact that 



are sisters, mig 



