GYMNOSPERMS. 163 



It is interesting to note further that in neither Cycas, Zamia, nor 

 Ginkgo was the stalk or prothallial cell of the pollen tube found in 

 the egg by any of the observers mentioned. These cells are probably 

 disorganized beyond recognition when the contents of the tube are 

 discharged into the egg. 



PINUS. 



THE MALE AND FEMALE GAMETOPHYTES. 



Apart from the absence of motile spermatozoids and the behavior 

 of the male gametophyte, the process of fecundation in the Coniferales, 

 so far as this is well known, is in general similar to that in Cycas, 

 Zamia, and Ginkgo, and it will be necessary only to point out briefly 

 the more important features of difference. 



Since the important researches of Strasburger, Goroschankin, and 

 Belajeff upon certain of the higher Gymnosperms, an interesting series 

 of facts has been collected by Dixon ('94), Blackman ('98), Cham- 

 berlain ('99), Murrill (1900), Ferguson ('01), and others. The studies 

 of later observers, who used more improved technique, have been 

 confined principally to the genera Pinus, Picea, and Tsuga, and 

 consequently our knowledge of the sexual process in many other 

 Gymnosperms is sadly wanting. 



It has been shown by Strasburger ('92) and others that the prothal- 

 lial cell in the ripe microspore of Pinus and other closely related genera 

 is the last one of a series of two or three cells, and that this cell divides, 

 as in Cycas and Ginkgo, to form the stalk cell and the generative cell 

 of the antheridium (Fig. 68, A, B). The generative cell (body cell) 

 then divides to produce the two non-motile male gametes, each consist- 

 ing of a nucleus surrounded by a specially differentiated mass of cyto- 

 plasm (Fig. 68, C). 



Contrary to Cycas, Zamia, and Ginkgo, the distal end of the male 

 gametophyte, or pollen tube, grows in a more or less direct line from 

 the pollen chamber down through the nucellus to the archegonium, 

 and while the tube seems to be merely a carrier of the gametes, it can and 

 doubtless does act as an absorber of nutriment as well. The probable 

 need of less food by the male gametophyte of the higher gymnosperms 

 may account for the absence of a specially developed absorbing appa- 

 ratus. This idea is advanced merely as a suggestion and not as an 

 adequate explanation of the difference between the behavior of the 

 tube of Pinus, for example, and that of Cycas or Ginkgo. Other 

 factors may have been more influential during the phylogenetic develop- 

 ment of these forms. 



