168 ULOTHRICACEAE 
but containing scattered granules of starch. Cell-wall composed 
of layers of cellulose which, for the dispersal of zodspores, pull 
apart in such a way as to leave sections which appear like a letter 
H in optical section 
Asexual reproduction by means of 2- or 4-ciliate zodspores, 
one or two in each cell; also by means of 2-ciliate microzoö- 
spores, several formed in a cell (gametes?) ; germination of both 
kinds direct. Akinetes and aplanospores are also produced. 
Inhabitants of fresh water. Type M. floccosa (Vauch.) Thuret. 
[Etym. yexeos, small, and ezopá, spore. ] 
Thuret separated this genus from Cozferva on account of the 
squared appearance of the chromatophore and the method of dis- 
persal of the zoospores, namely, by the pulling apart of the 
halves of the cell-wall. 
Both genera were recognized by Rabenhorst (63, '68) and by 
Wolle in his earlier study, as is evidenced by his published lists and 
by labels in his herbarium. Wille ('8r), taking no account of 
chromatophore form, but making an elaborate study of exsiccatae, 
reunited Microspora with Conferva because he found that in certain 
species left in Conferva (Tribonema) the structure of the cell-wall 
is similar to that described for JZzrospora. It remained for Lager- 
heim (87, '89) to define properly both genera by their chromat- 
ophore characters and assimilation products. 
A great effort has been made to furnish a contribution to the 
meager knowledge of the reproductive processes in this genus, 
but it is a matter of great difficulty to obtain zoóspores in any 
species. We have seen them produced only in two cases, in 
Microspora floccosa and M. stagnorum. In the case of the former, 
only a single filament was forming zoóspores, and the number ot 
cilia could not be made out, though the specimen was immediately 
fixed in osmic vapor. In M. stagnorum the zodspores, which did 
not seem at all like gametes, had only two cilia, whereas they are 
usually said to be 4-ciliate. 
Akinetes are frequently seen in most of the species. The 
filaments become moniliform, the cell-wall thickens and finally the 
cells fall apart as globose bodies, which, in the mass, resemble 
resting cells of Chlamydomonas. It is probable that these akinetes 
usually go through a period of rest before germinating. 
