[Vor. 1 
36 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
side of the vessel, are produced in large numbers. Plates made 
with this material yield an occasional pure culture, but most of 
the gametes fail to develop. It is impossible at present to say 
whether the colonies develop from newly formed zygotes or from 
gametes which fail to conjugate. 
Stigeoclonium tenue (Ag.) Kützing.— The ease and certainty 
with which zoóspores can be induced to develop in this form, 
and their extreme abundance, makes it, although a filamentous 
alga, an especially easy one to isolate. Freshly collected and 
thoroughly washed filaments of Stigeoclonium, placed in dis- 
tilled water or sterile nutrient solution, will, in from twelve to 
twenty-four hours, develop a great abundance of zoóspores. 
Cultures prepared in this way contain so small a number of 
bacteria that plates containing a hundred or more Stigeoclonium 
zoóspores are sufficiently free from bacterial colonies to 
render numerous successful pure transfers possible. Although 
a filamentous form, Stigeoclonium grows exceedingly well on 
the mineral nutrient agar. While other members of the 
Chetophoracee were not experimented with, it is reasonably 
certain that forms like Microthamnion, Chetophora, and Drapar- 
naldia, all of which readily yield large quantities of zoóspores, 
may be obtained in pure culture by a method identical with or 
similar to the one employed in the isolation of Stigeoclonium. 
Oedogonium sp., and Vaucheria sp.—While neither of these 
forms were obtained in pure culture, the observations made 
render it altogether likely that this will be possible when a little 
more attention is given to the cultural solutions. Repeated trials 
with the vegetative filaments demonstrated that from the 
latter no pure cultures could be obtained directly. The 
oóspore proved equally unsatisfactory because the oógonial 
wall is covered with adhering bacteria. Again, the odspore 
is, in most cases, so firmly and completely united with the oógo- 
nial wall that its separation from the latter is at present impos- 
sible. In both forms, however, zoóspores are readily obtained, 
and preliminary experiments demonstrated that these, like 
zoóspores in general, are bacteria-free. Where zoóspores could 
not be obtained in large quantities, individual ones were isolated 
with sterile pipettes, washed repeatedly in sterile water, and 
then either plated in the usual manner, or introduced into а 
