1190 Wisconsin Academy of Sciences, Arts and Letters. 
from cylindrical to spherical. Later he found that culture 
media with low osmotic pressure but containing traces of toxic 
substances, as copper or silver salts (27), or certain bog extracts 
(28), produced a change from the filamentous to the “Palmel- 
la” condition. 
By growing Scenedesmus in mineral solutions of different 
concentrations I have also found that with the increase in the 
concentration there is a tendency for the cells of the coenobe to 
become spherical, this tendency being much more marked in 
Scenedesmus quadricauda than in S. acutus. In S. acutus I dp 
not have the cells approaching so closely to the spherical as Senn 
(35 s ) finds them. I have also found that in the more concen¬ 
trated solutions the cells are much more apt to be abnormally 
shaped. The different forms produced in the concentrated solu¬ 
tions by S. acutus are shown in Plates LXXXYII and 
LXXXVIII, the colonies of S', quadricauda grown under the 
same condition in Plate LXXXIX. 
In both of these algae there are two classes of malformations. 
One class consists of irregularities in the individual cells, mal¬ 
formations of this type being given in Figures 47, 60, and 61. 
Advanced cases of this sort lead to greatly distorted coenobia. 
In the other class there is almost a complete loss of the coordi¬ 
nate axial arrangement, although the cells of the coenobe re¬ 
main attached in an irregular mass. These abnormalities are 
especially abundant in colonies containng eight cells. It is al¬ 
most impossible to classify these abnormalities, as an examina¬ 
tion of Figures 48, 54, 55, and 41 shows. This general arrange¬ 
ment of the colony is comparable to the “Palmella” stage of 
Stigeoclonium, although the use of the term “Palmella” is per¬ 
haps hardly applicable to Scenedesmus. We have, however, the 
same sort of response to similar changes in extreme conditions 
that Livingston obtained with Stigeoclonium. The response is 
not so general, only occurring in isolated cases. 
The experiments show that external conditions cannot cause 
a change from one type of coenobe to another. There may be 
changes in the individual cells of the coenobe, or an almost com¬ 
plete inhibition of the development of the colony in its ordinary 
