1909] ATKINSON—FUNGUS PARASITES OF ALGAE 323 
be absent. The penetration tube of the zoospore forms a short stalk, 
_ which projects but a short distance within the cavity of the host cell. 
This rudimentary condition of the rhizoids recalls that of Harpochy- 
trium hedenii Wille, though in the latter it penetrates only the outer 
lamella of the wall and flattens 
out in the form of a disk in the 
middle lamella, or merely pene- 
trates a thin layer of slime on the 
host and flattens out on the outer 
_ wall (ATKINSON 1903). This 
_ penetration tube serves also as 
_ the absorbent organ for such food 
_ as the plant obtains from the 
4 fluids within the gametangium of 
_ the host surrounding its zygo- 
spore. The zoosporangium 
measures 21-24 “, while the zoo- 
Spores are about 3 » in diam- 
eter, with a single cilium and a 
Fic. 2.—Rhizophidium brevipes Atk. 
A mature zoosporangium crowded with 
zoospores, outer layer of wall at exit pore 
dissolving, inner layer projecting as a 
papilla before the rupture, plants attached 
to a gametangium of Spirogyra contain- 
ing zygospores; B zoo i 
C two zoospores, unable to escape by exit 
pore, have germinated and are attempting 
: Prominent oil drop. 
The species was first observed 
_ Mma cell preparation which was 
: made on April 24, 1895, at about 
_ 4%.M. The zoosporangium was 
_ mature and the protoplasm finely granular. In the course of half an 
si hour from the time of the first observation, the granules began to 
_ 4iTange themselves in numerous small groups, the beginning of the 
formation of the zoospores. Very soon these began to disappear and 
_ Were gradually replaced by a prominent oil drop for each group of 
Stanules. Each oil drop was surrounded by a hyaline mass of homo- 
8&neous protoplasm. The preparation was watched for the greater 
: part of the time from 4 p. M. until 6 P. M., and fresh water was fre- 
7 quently drawn in, in order to hasten the development and maturity 
Of the zoospores. At this time it appeared that the zoospores would 
_ hot become mature under an hour, and the preparation was placed 
q ‘na moist chamber until 7 p.m. It was then examined and fresh 
_ Water added. The apical portion of the outer wall was dissolved; 
in the apex of the tube; D same 
showing how the zoospores retreated from 
the first tubes and after swarming around 
for the second time attempted to escape 
again by the germ tubes. - 
