278 Trow,— Observations on the Biology and 
work of hyphae forming a felt-like mycelium, and the forma- 
tion of the reproductive organs commences. These are of 
two kinds, asexual and sexual, of the type characteristic 
of the genus, and they appear in abundance in these cultures 
in the usual succession. We have first a crop of conidia and 
then a crop of oospores, the change from one type to another 
being quite gradual however, so that on adjacent hyphae 
conidia and oogonia may be seen in course of development 
at the same time. 
Formation of the conidia. The end of a branch stops 
growing in length, but grows in breadth so as to produce 
a spherical head ; this increased in size, and is finally cut off 
from the hypha which bears it by a transverse wall. Inter- 
calary conidia are formed in a similar manner. The proto- 
plasm of the conidia is about as dense as that of the young 
hyphae, and may or may not contain one or more vacuoles. 
Thus a conidium is simply a terminal or intercalary swollen 
portion of a hypha, cut off from the rest of the mycelium by 
one or two transverse walls. 
Formation of the sexual organs. An oogonium is at first 
exactly like a conidium. Even when it is cut off from its 
supporting hypha by a transverse wall, it requires some ex- 
perience to recognize it. It appears of a darker colour, due, no 
doubt, to the reserve materials present, but this is not apparent 
to the uneducated eye. Even a novice, however, is able to 
recognize an oogonium when it is accojmpanied by an antheri- 
dial branch or an antheridium. Fig. 3 gives the result of 
a study of the formation of the sexual organs up to the com- 
plete development of the antheridium. The observations 
commenced at 9.20 a.m. upon the two young oogonia 
shown in Fig. 3 a. The upper of these alone reached matu- 
rity ; the protoplasm of the lower and younger was used 
up to provide the material for the development of the older. 
In undisturbed cultures in Petri dishes this never happens, so 
that the anomaly is no doubt due to the necessary preliminary 
manipulation of the preparation. In four hours the oogonium 
had grown to its full size. At about 25 pm. the antheridial 
