[Vor. 1 
28 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
information the reader is referred to Moore (17), Richter (21), 
Küster (14), and others.) It is apparent that the large majority 
of forms isolated in pure culture belong to the Protococcales. 
Only a few of the filamentous forms, several diatoms, and but 
one or two species of the blue-green alge have thus far yielded 
to pure culture technique. 
PURE CULTURE TECHNIQUE 
GENERAL 
Algæ, generally speaking, are provided with a more or less 
highly developed exterior mucilaginous investment which may 
be either a distinct, separable sheath, as in many of the Cyano- 
phycem, ог merely a gelatinization resulting either from a 
modification of the external portion of the membrane, or from 
an internal secretion, as in some of the desmids. In general, 
also, algæ are slow growing as compared with many fungi. 
In these two characteristics most of the difficulties encoun- 
tered in pure culture technique among the algæ find their 
explanation. 
Among the fungi, spores with non-gelatinous walls are readily 
obtainable in a majority of the forms, and usually in great 
abundance. When such spores are plated in the way ordin- 
arily employed in bacteriological technique, a large number 
of colonies free from bacteria are usually obtained. Among 
the algæ, however, such non-gelatinous, resistant spores are, 
if produced at all, generally present only in small quantities. 
When vegetative algal cells are plated on a suitable medium, 
algal colonies will often be obtained, but they usually form the 
nucleus of a larger bacterial colony which has developed from 
the bacteria adhering to the gelatinous surface of the algal cell. 
Among those fungi in which spores are not readily obtained, 
an isolation in pure culture may frequently be effected by 
allowing the fungus to grow on a suitable medium until the 
hyphæ have outstripped the bacteria in their growth, at which 
time pure mycelial transfers may be made from the terminal 
portions. If, however, a like procedure is attempted with 
the algæ it will usually be found that the bacteria adhere tena- 
ciously to the surface of the growing filaments and are carried 
