214 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
• 
Very frequently, this connecting membrane is ruptured during the 
emergence of the zoospore mass, in which case some of the zoospores 
are liberated in the water while the remainder are left free inside the 
zoosporangium. The zoospores are finely granular, biciliate, and 
monoplanetie. The oogonia are borne in umbels on short con¬ 
stricted stalks in which cross walls are formed. The oospores are 
produced singly in the oogonia, are thick walled when mature, and 
during their development are surrounded by a cellular envelope 
derived from the periplasm. The antheridia arise laterally from 
special segments above the oogonia and, bending down, apply them¬ 
selves to the oogonia on the lower side near the basal stalk of the 
latter, which they perforate without indenting. 
The plants were found by Thaxter both at Cambridge, Massa¬ 
chusetts, and at Kittery Point, Maine, where they were collected in 
greater or less abundance during the late spring and summer. 
Biology. 
While collecting the material of Araiospora, some observations 
were made in regard to the habit and general conditions under 
which it lives, that may be noted here. It has both the habit and 
the situation of substratum of the /$'aprolegniaceae with which it 
is, in consequence, frequently found growing. The individuals of 
Araiospora, however, are usually shorter than the Saprolegniaceous 
forms and growing as they do in little, dense, cottony tufts, may 
readily be distinguished from the latter. These tufts are invariably 
about lenticels or other roughened places on the bark that form a 
suitable point of entry for the rhizoids. The plants have been found 
at the surface and as much as two feet below, on all sides of branches 
varying in size from twigs to limbs six inches in diameter. It is 
clear, therefore, that the zoospores, the agents for distributing the 
plant, are but feebly if at all heliotactic; otherwise, there would be 
a marked difference in the number of plants growing on the upper 
and under surfaces of these larger limbs. There is, furthermore, 
ample evidence that the oogonia and the antheridia are produced at 
a definite season of the year. During the month of April and a 
portion of May, and more particularly in the latter half of April, the 
plants produce the sexual organs in great abundance. At this time 
