CHAPTER XL 



SALVINIA NATANS. 



At the latter end of autumn the large ripe spores of 

 Salvinia form ellipsoidal cells whose longitudinal diameter 

 is from %" to J" ', clothed with a thick outer membrane in 

 which two layers are visible, the inner one being horny, and 

 the outer one granular and of a looser texture. At the apex 

 of the spore — that pole of it which is turned away from the 

 stalk of the sporangium — the outer membrane exhibits a 

 division into three lobes, the boundaries of which answer to 

 the edges of contact of the young spore with the three sister- 

 cells which were produced contemporaneously in the same 

 mother-cell. 



The contents of the spore look like a quantity of oil and 

 albumen. Spherical drops, both large and small, of a half 

 fluid substance, swimming in a thinner fluid, fill the inte- 

 rior of the spore. The apical portion of it is occupied by a 

 larger accumulation of the like mucilage. The history of 

 the development of the spore, which when half ripe appears 

 filled with delicate round vesicles, as well as the behaviour 

 of the above spherical masses dining germination, render it 

 not improbable that some at least of those large drops are 

 cellular formations filled with nutritive matter destined for 

 the germ-plant. 



Dming the winter the walls of the fruit perish. The 

 sporangia — as well those which contain one large spore each, 

 as those which contain small spores — fall from then stalks, 



