280 



THE AMERICAN NATURALIST 



[Vol. XL 



with the male nucleus, since the latter has been shown to be able 

 to unite with a purely vegetative nucleus, even of the sporophytic 

 generation. This observation of Miyake's seems therefore to 

 strengthen the evidence that the endosperm of angiosperms was 

 vegetative phylogenetically (Coulter and Chamberlain, :03, p. 183), 

 and to weaken correspondingly the view that it was strictly sexual 

 in its origin (Bonnier, :05) and that the endosperm is to be re- 

 garded as a modified embryo. 



If the introduction of the characters of the male parent into the 

 endosperm modified that endosperm so as to make it produce 

 food more suitable to the embryo with characters inherited from 

 the same male parent (Sargent, : 00, p. 708) then the embryo 

 would be more vigorous, and more fit to survive in the struggle 

 for existence than the one not nourished by such an endosperm 

 Hence those individual plants in which "double fertilization'* 

 took place would finally become dominant in the competition 

 with others of the same species. 



The reduction, disintegration, and final complete suppression 

 of the vegetative part of the male gametophyte may also depend 

 on the law of "use and disuse." The vegetative cells of a well 

 developed male gametophyte function chiefly in the process of 

 photosynthesis. In most of the gymnosperms this function is 

 impossible since the pollen grain is soon enclosed in the micropyle 

 and light is excluded by the thick scales of the fertile cone. It is 

 then a waste of energy and food materials to form cells that do 

 not function, and this waste is only in part compensated for, if the 

 cells formed disintegrate later and thus become available as food 

 for the work necessary in forming sperms. Disuse leads to disin- 

 tegration of the useless cells, and their complete suppression is the 

 most advantageous condition of all. 



wliifli pi-oh.-dtly lias the well dtnclopc^d male gametophyte, the 

 pollen lii-iiin does iioi (Miter the tnien»|»ylt> ('Thompson, : 05), but 

 goriiiinates at flie disiaJ end of die liiiiile, more or less entangled 

 on ils serrated edge. From this j)oiiit the {)ollen tubes pass in the 

 grooves on the surface of the ligule or scale, a distance of an inch 

 or more, to the micropyle. It would seem from this description 

 of Thompson's that the pollen grains are exposed to the light dur- 

 ing the development of the tubes, hence the multicellular male 



