1 90 Snow . — P seudo-P leurococcus , AW. 
That certain unicellular organisms are but phases of some 
higher Algae, assumed under some special condition, is now 
well recognized, and more and more is it evident that external 
conditions affect external characteristics. But it has been 
the result of my observation in all such cases, that the internal 
characteristics of a cell remain the same, however much 
external appearance may vary. Never have I observed the 
least variation in the internal organization of any species, 
although I have kept numerous unicellular and polymorphic 
forms in pure culture for many months at a time. With this 
in mind it is difficult to understand how Chodat can include 
under one species cells with and without a pyrenoid, and 
with either a parietal or a stellate chromatophore, as he does 
in the case of Pleurococcus vulgaris. 
The view held by Klebs, Artari, and Gay with regard to 
Pleurococcus vulgaris is undoubtedly correct, as I have been 
able to verify in Klebs’ own cultures and in numerous cultures 
of my own. There are, however, forms similar to that 
described by Chodat (2), which in their unicellular condition 
cannot readily be distinguished from Pleurococcus vulgaris, 
and which, under the influence of moisture, do produce fila- 
ments. But a close comparison of these forms shows differ- 
ences which would prevent them from being classified with 
Pleurococcus vulgaris. Whereas in the latter species the chro- 
matophore lines the whole inner surface of the membrane, in 
the corresponding small cell-complexes of the other forms 
the chromatophore is found in only a portion of the cell. 
Pletirococcus vulgaris , also, contains no pyrenoid, while in the 
filamentous forms which have come to my notice a pyrenoid is 
present. Chodat, however, found none in the form he studied. 
One significant difference between these filamentous forms 
and Pleurococcus vulgaris is the response to cultivation. The 
latter form lives but a short time in Knop’s solution of various 
concentrations, but under the very same conditions the forms 
which produce filaments grow well for any length of time. 
In referring to this form described by Chodat (2), Klebs 
regards it as a Stigeoclonium which normally exists in a 
