1196 Wisconsin Academy of Sciences, Arts and Letters . 
may reach 15 bv 20 microns. The shape of the cell varies 
from nearly spherical (Fig. 104) to ovoid (Fig. 103). The 
majority of the cells are ovoid. 
Chodat (9) has figured a large number of aberrant forms of 
Sce7iedcsmus quadricauda that were obtained chiefly on solid 
media, agar and gelatin, containing glucose, cane sugar, gly¬ 
cerine or some other organic compound. Some of his draw¬ 
ings show cells that are quite similar to what I have described, 
above for S. acutus, in that there has been the same sort of 
failure to complete the normal cleavage. He also finds that in 
some cells horns do not develop© in the usual manner, but 
thick buttons are formed instead. The cells bearing these but¬ 
tons are irregular in shape. Chodat finds that the outer gela¬ 
tinous covering of the cell wall may also be thickened, the 
covering showing a iamellated appearance in extreme cases. 
I have found that there is sometimes an inhibition of the 
formation of the characteristic horns. Some coenobia com¬ 
posed of giant cells have horns that appear quite normal (Fig. 
114), while others have no horns, or merely a small nodule at 
the ends of the terminal cells (Fig. 99). 
There is considerable fragmentation of the coenobia in cul¬ 
tures in solutions of high osmotic pressure and isolated cells 
are quite frequent. These single cells are usually giant cells 
rather than those of normal size. The formation of the free 
cells is due to the failure of the coenobe to form the gelatinous 
material that binds the cells together. Senn (35) has already 
shown that in Scenedesmus there is an inhibition of cell di¬ 
vision in the .jsre concentrated culture media. These large 
cells in my cultures are filled with oil and an immense number 
of starch grains. Apparently the concentrated medium does 
not hinder the process of photosynthesis, but does hinder the 
assimilation of starch after it is formed. This increase in 
size may be due, to a certain extent, to the formation of large 
amounts of starch. Unfortunately material from cultures con¬ 
taining these large cells was not fixed and stained, so that I 
am unable to state the exact nature of the cell contents: but 
from the appearance of occasional giant cells in normal cul- 
