6i6 Trow . — The Karyology of Saprolegnia. 
Cultures . It is obviously advisable to secure material which 
consists of a single species only. To obtain such, following in 
the main the method of De Bary (’88), samples of various 
aquatic plants, e. g. Algae, Mosses, Phanerogams, &c., are 
first collected from any convenient piece of fresh water. 
These are placed in small glass jars — marmalade pots answer 
well — and dead house-flies, previously wetted with alcohol 
and washed with water, are thrown on to the surface. Almost 
invariably some member of the Saprolegnieae is found grow- 
ing on the flies in the course of two or three days. The 
fungus produces a kind of halo of hyphae extending all round 
the submerged parts of the fly’s body. The sporangia, which 
are large enough to be detected by the practised unaided eye, 
rapidly make their appearance ; and later on, generally in 
about a week, the sexual organs are formed. 
When the sexual organs have produced ripe oospores, the 
purity of the culture may be roughly estimated. As a rule 
more than one species is present. If a suitable species has 
been found, it may be separated from those associated with 
it in several ways. The most effective method is to cut off, 
on a cover-glass, a small branch bearing oogonia ; wash away 
all spores and extraneous matter with water sterilized by 
boiling ; add the leg of a fly and a drop of water, and invert 
over a perforated piece of cardboard, which is made to rest 
on a glass slide and is kept thoroughly moist. The culture 
started thus, in a very simple and effective moist chamber, is 
kept under microscopic control for a day or two. The 
separated branch is not seriously injured by these manipula- 
tions, and generally puts out small branches which develop 
rhizoids and attack the leg of the fly. When it has been 
ascertained that the severed branch alone has infected the leg, 
cultures may be proceeded with on a large scale, as follows : 
Glass jars are sterilized by a dilute solution of mercuric 
chloride and thoroughly rinsed with water carefully sterilized 
by boiling. Sterilized water must naturally be used for the 
culture-fluid. If small glass squares are used to cover these 
jars, a large number may be prepared at one time and kept 
