1198 Wisconsin Academy of Sciences , Arts and Letters . 
> 
nearly spherical, is the nearest approach to a true “Palmella” 
condition that has been found in any of the forms studied. It 
is noteworthy that such a parenchymatous mass of cells is 
formed in response to exactly the same stimuli that Livingston 
used in his earlier work on Stigeoclonium (25) (26). 
ISToncoplanar Forms. 
} Tetradesmus, A Parallel Nonconcurrent Colony. 
Although when viewed from the standpoint of the classifica¬ 
tion of the relationships of the long axes of the cells, T&trades - 
mils is not very closely related to Scenedesmus, yet from the 
phylogenetic standpoint these two forms are very closely re¬ 
lated. This is especially true when Tetradesmus Wisconsin- 
ensis and Scenedesmus acutns are compared. I have shown 
(36) (37) that the manner of formation of the daughter colon¬ 
ies in these two forms is very similar, up to the point of the 
liberation of the young colony from the mother cell wall. At 
this point the young colony of Scenedesmus unrolls and the 
cells become arranged in a plate, while the colony of Tetradm- 
mus does not unroll but the cells retain the same relationship 
that they had within the mother cell wall. 
We should therefore naturally expect much the same varia¬ 
tions to occur in Tetradesmus as in Scenedesmus and this ex¬ 
pectation is realized. There is again the variation in both 
the individual cells and the arrangement of the cells in the 
coenobe. There is the same rounding up of the cells in con¬ 
centrated culture media that there is in Scenedesmus acutus . 
As in S. acutus the cells do not become completely spherical 
but retain their acute apices. The Tetradesmus cells are 
much more pointed at the apex than are cells of S. acutus when 
this rounding occurs (Fig. 118, Plate XO). 
Cells of coenobia grown in nutrient solutions of compara¬ 
tively low osmotic pressure also show variations from the 
normal. These irregularities may be either in the size 
or the shape of the cell (Figs. 116 & 117). The walls of 
the cell also show variations in that the end may form short 
blunt horns in some instances (Fig. 116). 
