326 BOTANICAL GAZETTE [NOVEMBER 
RHIZOPHIDIUM SPHAEROCARPUM 
Rhizidium sphaerocarpum Zopf, Nova Acta Leop.-Carol. Deutsch. Akad. 
47:202. pl. 19.. figs. 16-27. 1884. 
Rhizophidium sphaerocarpum A. Fischer, Rabenh. Krypt. Flora Deutschl. 
Oesterr. u. Schweiz 2 Aufl. 4:95. 1892 
What I have taken to be this species occurred in abundance on 
threads of Mougeotia parvula collected in a gutter on Thompson St., 
Ithaca, N. Y., April 7, 1895. The zoosporangia are oval in form 
and vary considerably in size, the larger ones measuring 16-18X 
18-20 #, while the smaller ones are about 1oX11 ¢. They occur 
singly or in groups of two to four, the smaller ones more commonly in 
groups and the larger ones rarely so. The rhizoids are very much 
reduced, consisting of a few very short branches from the short 
entrance tube. 
The wall of the zoosporangium consists of two lamellae, an outer 
stout lamella and a thin inner membrane. This is very well seen in 
the dehiscence of the zoosporangia. At maturity the apex of the outer 
wall of the zoosporangium dissolves, forming a large circular opening 
for the exit of the zoospores. Through this the inner membrane 
projects in the form of a short broad papilla by the swelling of the 
epiplasm. The final rupture of this membrane sets the zoospores 
free, and the large opening permits their rapid escape. The exit pore 
measures 5—6 » in diameter in the larger forms, and in the smaller 
ones is proportionately larger, being 4-6 w in diameter, some of the 
smaller zoosporangia appearing like cups when open. The zoospores 
are oval, possess a long cilium and a prominent oil globule, and 
measure 1.5-2 in diameter. In germination, if the germ tube 1s 
directed toward the wall of the host cell, it penetrates the wall, and 
then the zoospore enlarges to the size of the mature plant, becoming 
the zoosporangium. If, however, as sometimes happens, the germ 
tube is directed away from the wall, or along its surface, it may gTOW 
to a considerable distance, sometimes reaching a length of 30 - The 
zoosporangia sometimes grow so as to appear attached by their side 
instead of by their base, and the opening is then at the side (fig. 3; C). 
In nearly all of the larger specimens (which may prove to be 
a different species) the effect on the host cell was quite remarkable. 
The host cell not only becomes considerably larger near the middle, 
