176 



SALVINIA. 



in this country, is really quite abundant, but always in 

 cultivation. Few greenhouses in which there are tanks 

 of water plants are without it, and it has become domes- 

 ticated, as it were, in many-small ponds, fountains, and 



artificial lakes. 

 So far as known 

 it has s h o w n 

 no tendency to 

 spread to other 

 waters unless 

 its occurrence 

 at Os c h e r ' s 

 Salvinia natans. Lake is an in- 



stance. 



The main axis of Salvinia natans may reach a length 

 of two or three inches, but is usually shorter. Along 

 this the leaves are thickly clustered in several longi- 

 tudinal rows. Two of these rows on the under side of 

 the stem are finely dissected into 

 thread-like divisions, and go down in- 

 to the water functioning as roots, 

 since there are no true roots ; the 

 others float on the surface. These 

 latter are half an inch or less in 

 length, bright green, almost as broad 

 as long, with a very blunt tip, and 

 slightly heart-shaped base. Above 

 they are thickly set with very short, Sporocarps of Salvinia. 

 soft, branching hairs that, though apparently so insignifi- 

 cant, are of great importance to the plant, since they 

 keep it right side up in the water. It is practically im* 

 possible to make these plants float with the upper surface 

 downward, for the tiny hairs hold great numbers of air 



