ii8 HISTORY OF BOTANY 



Hofmeister next showed that in Pilularia, Salvinia, 

 Isoetes, and Selaginella there were two kinds of spore, 

 a smaller one giving rise to a male and a larger one to a 

 female gametophyte, the fertilised ovum of the latter 

 becoming once more the generation bearing the generic 

 name. In other words he elucidated the true significance 

 of heterospory, and followed out the differentiation of 

 sexuality in the gametophytes of the Pteridophyta. 

 Turning next to the Coniferae, he demonstrated that 

 the pollen grain in that group was the equivalent of the 

 microspore in the heterosporous Vascular Cryptogams, 

 while the embryo-sac and endosperm corresponded to the 

 megaspore and its contained female prothallus. The 

 homologies between the two stages in the Vascular 

 Cryptogams and the condition of affairs in flowering plants 

 now presented no difficulties, and the ovule was seen to 

 consist of a single megaspore permanently enclosed 

 within its sporangium, whose wall had become greatly 

 thickened and nutritive in function — Robert Brown's 

 " perisperm " — and had acquired additional integu- 

 ments, the whole enclosed in the carpel or modified 

 sporophyll. 



The chief effect of all these fundamental discoveries 

 was to show that the key to a true natural classification 

 lay not in the balancing of values among the various 

 morphological parts of the flower and fruit, but in a 

 detailed study of the anatomy of the real and concealed 

 reproductive organs, rather than of the more obvious 

 pseudo-organs of multipUcation. How great was the 

 change in the whole outlook we shall see later on ; mean- 

 while the splendid results achieved by Hofmeister were 

 the means of turning the attention of a host of investi- 

 gators to the group that had yielded such a harvest of 

 illuminating ideas, the hitherto despised and neglected 

 Cryptogams. 



