524 A Q UA TIC PH YCOM YCETES 



varying in size (average variation from 9-23 \x), was never larger than 

 the operculate sporangium; (3) the sporangium maintained the same 

 general shape (usually subspherical) at all times, but exhibited striking 

 variations in size when growing on different algae. On Rhizoclonium the 

 sporangia averaged 29 u. (limits of variation 20-35 jjl); on Spirogyra, 8[x 

 (6-11 (A); and on Oedogonium, 13 \x (12-15 \x). These variations were 

 not necessarily coordinated with differences in the diameter of the algal 

 cell, for though the largest sporangia were formed on the alga having 

 the largest cells (Rhizoclonium) the smallest were not formed on the 

 most slender filaments (Oedogonium), but on Spirogyra. The rhizoidal 

 system also underwent marked variation on the three algae, being ex- 

 tremely stout and well developed in Rhizoclonium, very sparse in Spiro- 

 gyra, and either so tenuous as to be invisible or entirely lacking in Oedo- 

 gonium. 



Karling grew the fungus on a variety of Conjugatae and other green 

 algae as well as on Chara and Nitella, all of which had been killed by 

 boiling. No quantitative or qualitative data are given for the fungus on 

 these different substrata. His successful efforts to cultivate it saprophyt- 

 ically makes Karling inclined to doubt that the species is at all parasitic 

 and also makes him question the validity of the cross-inoculation 

 experiments mentioned above so far as they indicate actual parasitism 

 of the three hosts. The purpose of these experiments was not primarily 

 to test the range of parasitism, but rather to observe morphological 

 changes in the fungus when it was growing on different algae. It might 

 be emphasized, however, that while the environment of a van Tieghem 

 cell is not a natural one, it is not necessarily unfavorable, and that in 

 both controls and infected cells the algae not only appeared healthy, 

 save where attacked by the zoospores of the fungus, but showed evi- 

 dences of cell division and growth. The demonstration of saprophytism 

 is direct and certain; it is not, however, evidence which necessarily 

 disproves a fact noted in many other fungi, namely, that they may at 

 times also attack a viable organism. 



From these researches it is certain, at any rate, that the species can 

 exist on a fairly wide variety of substrata, and in view of this circum- 

 stance it is surprising that it has not been recorded more often. Such 

 studies as have been made on Chytridium lagenaria, especially those 



