[Vor. 4 
274 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
cell itself. While these localized growths of the wall are 
usually external (pl. 18, figs. 2-4), they may likewise be in- 
ternal (pl. 18, fig. 6), and although both the wall and these 
growths usually show a characteristic lamellate structure they 
may be entirely homogeneous. 
Calcium oxalate crystals were infrequently observed within 
the cell (pl. 18, fig. 14). 
The only type of reproduction observed was by aplano- 
spores, which are freely formed throughout the growing 
season. ‘These may be produced in cells which are circular 
in outline, but usually the sporangium is formed from a cell 
which is considerably longer than broad and on the wall of 
which a distinct excrescence has formed. The aplanospores 
are produced by successive division (pl. 18, figs. 7-11), and 
usually number from 32 to 64 in each sporangium. They are 
practically spherical and measure about 4 д in diameter. By 
the time the aplanospores are completely formed there is 
frequently produced a distinct opening in the sporangium 
wall quite large enough to permit the escape of the spores. 
This opening may occur at any place in the wall but has 
occasionally been observed at the end of a tubular extension 
of the cell (pl. 18, fig. 12). Generally it is a distinct pore 
produced by the dissolution of the wall at that point but at 
times a considerable portion of the wall may be cut out and 
turned back in an irregular manner, suggesting somewhat the 
method of spore liberation in Chlorocystis (pl. 18, fig. 13). 
In spite of this provision for the escape of the spores, they 
rarely take advantage of it—in fact any aplanospores which 
leave the sporangium through the opening provided appear 
to have done so entirely by accident. 
Usually the spores remain clustered together in about the 
position in which they were formed. Аз they increase in 
size the old sporangium wall disintegrates, and the new plants 
are gradually distributed through the gelatinous matrix of 
the Rivularia by the formation of new filaments of the blue- 
green and the action of such forces in the water as would 
be calculated to break up the original arrangement. The very 
definite provision for a means of escape for the spores sug- 
