102 MICROSCOPY FOR BEGINNERS. 



float out and roll away through the water, revolving as 

 they are often seen to do even before leaving the parent. 

 The water in some localities is, in June, so filled with 

 these rolling globes that it is colored green by them, 

 and when the collecting-bottle is held against the light 

 they become visible to a sharp eye as small pale-green 

 spheres. The diameter of a full-grown plant is about 

 one-fiftieth of an inch. V. ylobdtor. 



4. HYDKODICTYON (Fig. 81). 



A yellowish-green scum is sometimes seen on the wa- 

 ter, which, when spread out over the fingers, proves to 

 be a net of delicate green 

 meshes. It may grow to 

 ten or twelve inches in 

 length, and form floating 

 masses several inches in 

 thickness. The nets are 

 composed of narrow short 

 cylindrical cells. Under a 

 low power they 'are re- 

 markably beautiful. The 



Fig. 81. Hydrodictyon ntricnlfitnra. 



figure shows a part of a 

 net. II. utriculdtum, Tig. 81. 



The masses which the Algae form are usually com- 

 posed of great numbers of long threads, commonly 

 called filaments, and matted together, probably by their 

 rapid growth, among other causes. Each filament is 



