Jan. 1902.] BOTANICAL SOCIETY OF EDINBUKGH 151 



becomes sterilised to form a sexual individual or game- 

 tozoon. Their remaining together, and the continued and 

 progressive amplification of the gametozoon in course of 

 ages, have naturally deferred their ripenings, sex-deter- 

 minations, and reductions to later and later periods. It is 

 obvious that this could easily be efiected by starving them, 

 but this may not have been Xature's method of delaying 

 their ripenings. A potent factor has probably been delay 

 in the period of the determination of sex. 



In the higher plants it is the spores, whose name is 

 legion ; while the " sexual cells," eggs and sperms, are few 

 and far between. In animals the " sexual cells " exhibit 

 the reverse condition, corresponding in their multitude to 

 the spores of plants ; while, as we at length know, the 

 spore-mother-cells — there are no spores in the ]\Ietazoa — 

 are not very numerous, being represented in some cases by 

 but one cell in addition to that which forms the sexual 

 generation. 



^Miy this difference?^ In the embryo-sac of Finns, 

 which is the gametophyte, there are only four germ-cells. 

 In the corresponding structure in flowering plants there 

 are perhaps three, or at most six ; while, as is well known, 

 the male gametophyte of a flowering plant is represented by 

 one or two vegetative cells and one or two germ-cells. 



Xo Metazoan sexual generation has so small and scant 

 an endowment as these, while such an animal may contain 

 and harbour a number of germ-cells thousands of times 

 greater. 



The difference is solely due to the different procedure 

 adopted at the formation of the primary germ-cells or 

 spore-mother-cells. The plan carried out in animals has 

 been such as to favour and foster the ever greater and 

 greater amplification of the sexual generation. In plants, 

 as elsewhere already insisted, the reverse is the case. 

 Here the asexual generation has undergone increased 

 amplification without ever being able to attain any very 



1 " Zu vielen Tausenden zaehlen die vegetativ erzeugten Sporeu, 

 welche ein einziges Farnblatt ausstreut. Bei der geschlechtlichen 

 Fortptlanzung der folgenden Generation wird dagegen von einem 

 Prothallium selten mehr als ein neues Einzelwesen gebildet, etc." — 

 F. Noll, in Strasburger's " Lehrbuch der Botanik," 2 te Aufl., 1895, 

 p. 255. 



