THE SALVINIACE^. 



I?' 



Cross-section of Salvinia 

 sporocarps. (Enlarged.) 



urn-like inckisia of the filmy ferns should completely 

 enclose the sporangia. In Salvinia the sporocarps are 

 borne on the submerged leaves, usually in clusters of 

 three ; in A:iona they are borne in pairs in the axils of 

 the aerial leaves. Some of the sporocarps in each cluster 

 of Salvinia always bear megasporangia. There are about 

 ten in each sporocarp, and each megasporangium bears a 

 single large ovoid megaspore. The 

 microsporangia are more numerous, 

 globose, and contain a large number 

 of microspores. In Azolla the pairs 

 of sporocarps are usually of two 

 sizes, the smaller beaiing a single 

 megaspore, and the larger producing several microspo- 

 rangia and numerous microspores. The mature sporo- 

 carps drop from the plant and promptly sink to the 

 bottom of the water, where they continue to enclose the 

 spores for some time. The latter are finally liberated by 

 the decay of the walls surrounding them. The micro- 

 spores of yJ.^c//« are usually held together by 

 a solid sort of protoplasm which produces 

 hooked processes from the outer surface. 

 The sporocarp appears to be an outgrowth 

 of the leaf that, beginning with a ring sur- 

 rounding the sporangia, slowly increases 

 until it has completely enclosed them. Before this has 

 happened, however, certain algae take up their abode in 

 the sporocarps, and when the latter mature they go into 

 a j-esting condition, forming little colourless spheres. 

 These spheres are seldom absent from the ripe sporo- 

 carps. 



The genus Salvinia was named for Salvini, a Floren- 

 tine professor. There are about a dozen species known 



Sporocarps of 



Azolla. 



(Enlarged.) 



