1907] YOUNG— MALE GAMETOPHYTE OF DACRYDIUM 195 



saw a small nucleus which he thought to be the stalk nucleus. From 

 MicrocycaS; then, through Dacrydium to Pinus we have a reduction 

 series in the spermatogenous tissue. The inequahty of the sperms, 

 so common in conifers^ is only a further step in this reduction. 



The tendency for two body cells to develop in Dacrydium may be 

 related to the transverse division of the generative cell. In Pinus 

 the inner cell has the advantage at the start, and is thus set apart as 

 the body cell; but in Dacrydium both cells begin cxslstcnce wiih 

 apparently even chances, being equally free to enlarge. Thus it 

 seems at first a matter of indifference which shall be the body cell 

 and which sterile, and some accident of slightly superior size or 

 better nourishment may be the determining factor. 



SUMMARY 



1. There are two prothallial cells cut off from the main body of 

 the spore. In Dacrydium Bidunllii usually only the second divides; 

 in D. laxijolium and D. cupressinum both divide. 



2. The generative cell divides by an anticlinal wall, one daughter 

 cell functioning as a body cell and the other being sterile. In some 

 cases both produce body cells. 



3. The walls of the prothallial cells and the two generative daughter 

 cells disappear. 



4. The mature pollen grain contains the body cell and five or six 

 free nuclei, according as the first prothallial cell has or has not 

 divided. 



under the direction of Professor J 



Coulter and Dr. C: J. Chamberlain. 



University of Chicago 



Note, — Since this investigation was completed, a paper by Jeffrey and 

 CjaRYSLER (The microgametophyte of the Podocarpincae. Amer. Nat. 4^* 

 355-364- 1907) on the same subject has appeared. The paper deals chiefly 

 with Podocarpus, The development of the gametophyte corresponds in general 

 with that of Dacr}'dium, but with further divisions of the prothallial cells, resulting 

 sometimes in eight, and an occasional division of the generative cell into three 

 instead of only two cells. 



