maximum periods ; one occurring in the spring and the other in the 

 autumn. 



One of the most important factors which determine the occur- 

 renc of species is the height of the water. An increase of one or 

 two feet in the height of the water during the spring and summer 

 months over that of a normal season will completely shut out for 

 that season many forms of aquatic plants. During seasons of 

 abnormally high water we have looked in vain for certain species of 

 Nitella and Algae, although they were abundant both before and 

 after such seasons. The high water changes the light conditions 

 which are so essential to certain species that they are incapable of 

 developing. 



Most of the species of filamentaceous Algae in this list have been 

 preserved upon microscopic slides. The most satisfactory preserv- 

 ing fluid for this purpose we have found to be one made up as 

 follows : 



Glycerine, i part 



Water, 2 parts 



Alcohol, 3 parts 



The specimens to be mounted are placed in small amounts of this 

 solution contained in a watch glass where they are left until the 

 water and alcohol has evaporated. After this has taken place they 

 are laid on a slide and ringed and sealed. When this process is 

 carried through rapidly, that is in three or four hours, and the speci- 

 mens kept in the dark, they will hold most of their color and form 

 tolerably well for many years. 



G. E. STONE. 

 Mass. Agricultural College., July i, i8gg. 



