iqis] HUTCHINSON— MALE GAMETOPHYTE OF PICEA 297 



Relationships 



No one character is sufficient to establish relationships of plant 

 groups. Since similarity of male gametophytes gives only one- 

 sided evidence for the relationship of species or genera, the dis- 

 cussion will be limited to comparison of types. In Taxodineae and 

 Cupressineae the gametophyte consists of an antheridial cell, 

 which may divide before or after shedding, and a tube nucleus; 

 no evanescent cell is present. Similar gametophytes are found in 

 Picea canadensis (fig. 30). In cycads two cells are cut off from the 

 primary cell, one of which is antheridial (cf. fig. 38). The shedding 

 stage characteristic of the abietinean gametophyte (also of Ginkgo 

 and Ephedra) contains two more or less evanescent cells and an 

 antheridial cell, which may or may not divide, beside the tube 

 nucleus (cf. figs. 50, 51, 52). The podocarp type is similar, but 

 the polar cells are not evanescent and frequently divide (cf . figs. 39, 

 40, 52). A massive polar tissue containing free nuclei, which 

 Lopriore (18) regards as antheridial, is characteristic of the 

 araucarian type. A similar gametophyte is shown in fig. ^^. The 

 male gametophyte of Picea canadensis is in a state of unstable 

 equilibrium. Slight differences in conditions are sufficient to shift 

 the balance in one of several possible directions. The resulting 

 forms correspond to the various types of gametophytes found in 

 gymnosperms. 



Summary 



In the male gametophyte of Picea canadensis, one, two, or three 

 potentially antheridial cells are cut off from the primary cell; one 

 of these divides to form a spermatogenous and a sterile cell; the 

 others, when formed, are more or less evanescent. Occasion- 

 ally there are two functioning antheridial cells, resulting in a bi- 

 antheridial gametophyte. 



The writer is indebted to Professor John M. Coulter, 

 Dr. Charles J. Chamberlain, and Dr. W. J. G. Land for many 

 suggestions and criticisms. 



University of Chicago 



