' f 



194 



BOTANICAL GAZETTE [September 



name 



lum 



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with 



In IMicrocvcas the genera- 



tive cell produces the sterile stalk cell and eight or more body cells 



Cup 



o 



cells divides many times, giving rise to extensive fertile tissue. J 



tive. In fact, all the early figures up to the five-cell stage might be j 



taken to represent Dacrydium cupressinum. These show the forma- \ 



tion of first and second prothallial cells, the generative cell, and the 

 division of the first prothallial cell. According to Lopriore's account, 

 howeverj after the first two divisions it is usually the middle, that is 

 the second prothallial cell, which divides longitudinally, cutting off 

 what we would call the generative cell. 



■ The complex in Cupressus is not at all comparable to that of Arau- 

 caria, for it has a wholly different origin. It is not formed early in 

 the histor}^ of the gametophyte by successive divisions of the spore, 

 but later, in the tube, by the division of a single differentiated repro- 

 ductive or body cell. The rarity of any prothallial cells at all in 

 conifers sets apart Abietineae, Podocarpineae, and Araucarineae as 

 the possible representatives of a more primitive condition. Araucaria 

 seems to point toward an ancestral functioning thallus, and Dacrydium 

 shows a further step in the reduction so nearly accomplished in 

 Pinus. A possible connection between the three groups is suggested. 

 The question of relationships, however, can be answered only through 

 the combined results of various lines of research. 



In most conifers that have been studied, the generative cell divides 

 periclinally to form the so-called stalk and body cells, but outside 

 of conifers we fmd Cycas and Ginkgo in which the division is trans- 

 verse. The term ''stalk cell" is a rather unfortunate one. Its use 

 was suggested by the position of the cell between the body and the 

 prothallial cells, but in the case of a transverse division, or where, as 

 in Sequoia and Cr}^ptomeria, the division takes place in the free 



is entirely lost. 



It is perhaps misleading, too, in the suggestion of the stalk of an 

 antheridium. 



The generative cell is the first of a spermatogenous series. In 

 Pinus, for example, it divides, giving rise to a sterile and a fertile 

 cell. The body cell divides once and produces two male cells. In 





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