136 : BOTANICAL GAZETTE [FEBRUARY 
find what another has reported in a given species, may be due to 
variations in the conditions of the environment at the time of 
collection, the effects of which are almost entirely unknown at the 
present time. From the very character of the work, such errors 
are peculiarly liable in cytological investigations, for it is mani- 
festly impossible within reasonable limits of time to examine 
thoroughly material taken under various conditions of growth over 
a series of years. 
The question of species 
On account of the great distances separating the three known 
habitats of Rhodochytrium and the diversity of its hosts, one is 
led to suspect that there are three species rather than one. With 
the idea of separating them if possible, a study was made of 
LAGERHEIM’S and of BARTHOLOMEW’s collections. Previous com- 
parison of the North Carolina material with LAGERHEIM’s descrip- 
tion had disclosed some minor differences, but these disappeared 
on examination of the plant itself. In the form on Asclepias, 
likewise, I am entirely unable to detect any constant or significant 
differences. The various figures presented herewith show how 
difficult it is to find characters in Rhodochytrium. In size and shape 
there is every possible variation, and there is a total absence of 
such peculiarities as markings on the spores, etc., which in many 
groups supply useful specific characters. 
It was thought for a time that the shape and size of the plugs 
which close the mouths of the zoosporangia were different in the 
three forms. LacERuemm describes the original R. spilanthidis as 
having a bell-shaped plug (cf. fig. 21) which did not develop until 
the sporangium had reached a considerable size. In the form on 
Ambrosia the plug is generally 25-35 long, solid, and develops 
early (fig. 14). The form on Asclepias has a similar plug, but it 
is usually larger, reaching a length of 60 » (fig. 16). The condition 
ofall the plugs in the 1908 material was fairly constant, but the 
1910 material showed such variation that it became evident that 
the characters of the plug were worthless. Its size varies with 
that of the sporangium. In large sporangia on the stem it some- 
times reaches 50 in length, and in small ones on the leaves it is 
