KS 
Such pure growths are quite infertile, however, and remain 
so for months or years, though we can obtain zoospores or 
oospores at any time in a few hours by transferring a piece to 
water or food materials in water. It is interesting to note that 
Trow* has recently applied a similar method for obtaining pure 
cultures of a Pythzum, modifying the procedure in so far that he 
obtains his material from the erial hyphze developed from the 
surface of the solid material. 
Having isolated our fungus, the next step is to cul- 
tivate it as a pure growth, and here we may aim at 
either one of two objectives: we may (1) wish merely 
to grow the fungus successfully in masses and observe its 
behaviour, much as a gardener desires to see the effect of a bed 
of annuals which he sows thickly, or (2) we may want to trace the 
details of germination and development of a single spore and 
plant under the microscope, much as a physiologist focusses his 
attention on a single plant grown from seed in a pot. 
In illustration of the first case; among the more troublesome 
forms which can, nevertheless, be cultivated, may be mentioned 
the various wood-destroying Hymenomycetes—e.g., species of 
Stereum, Collybta, Armillaria, &c. The principal difficulty in 
these cases 1s to obtain the isolated specimen to start with, but 
having obtained that its further growth is ensured by transferring 
it to a block of wood—due regard being had to the species it 
was found growing on—resting on a little moist cotton wool in a 
plugged tube, and thoroughly sterilised by heating in a steamer. 
It by no means follows that you will bring such cultures to a 
successful issue, however, and I may take this opportunity of 
saying that the cultures of Marasmius androsaceus referred to in 
my last addresst have not even yet, after two years culture, de- 
veloped any trace of pileus. They are still alive, and appar- 
ently growing, but they yield no fructification. In the choice 
of food-materials, attention should be paid to what is known of 
the habits of the fungus. Most saprophytic fungi will endure, 
or even prefer, an acid medium, and in many cases this helps us 
to subdue intermixtures of bacteria on the isolation plates; 
but some—e.g., Saprolegnia—are easily killed if the medium 
becomes acid. Again, it is a rule that fungi growing on dung 
or other animal débris succeed better on gelatine media with 
extracts of dung, &c., than do saprophytes normally met with 
on decaying fruit, roots, or other vegetable tissues. Indeed, I 
sometimes find that gelatine—an animal substance—acts like a 
* Ann. of Bot., 1901, vol. xv., p. 269. 
+ Pp. 139-40. 
