FRESH-WATER ALG^ OF THE UNITED STATES. 87 



grow, and, at the same time, separate from one another. Whilst these changes 

 have been taking place the spore coat has been becoming gelatinous and enlarging, 

 so that it continues to enclose its progeny. In this way a family of oval cells is 

 formed (fig. 4 b, pi. 7). So far, I think, is positive. The next step I have never 

 actually seen, but believe to be the escape of these oval bodies as zoospores (fig. 

 4 c, pi. 7) which are of very various sizes and are elliptical, globose, or oval. They 

 have a tolerably well-marked bright vacuole at their beak, and after swimming 

 about actively for a time finally settle down, lose their cilia, and undergo division. 

 They seem often to cluster together before thus becoming quiescent, so as to make 

 little colonies (fig. 5, pi. 7). 



Genus CHLOROCOCCUM, Fries. 



Cellulffi sphffiroideae, aut singulae, liberce, vesicula chlorophyllosa et locello lateral! pallidiori cavo? 

 instructs, limbo hyalino et tegumentis saspe amplissimis ciuctee, aut plures in stratum vel acervulos 

 cumulatse. 



I'ropagatio fit zoogonidiis cytioplasmatis divisione ortis, e cytiodermatis abavise (intellige tegu- 

 mcutum extremum) rupturis escedentibus. 



Cells spheroidal, cither single, free, furnished with a ehlorophyllous vesicle and a paler lateral 

 (hollow ?) spot, with a hyaline nimbus and surrounded by a wide coat ; mostly accumulated together 

 into strata or little heaps. Propagation by means of zoospores, which are formed by a division of 

 cytioplasm and escape from their general tegument (the cytioderm of the original cell). 



Remarks. — But a few weeks after the commencement of my study of fresh- 

 water algse, a friend, a young microscopist, asked me to look at his aquarium, as 

 the water of it had become stagnant, opaque, and green. On examining a little 

 of the water with the microscope it was found to be fidl of what I now know to 

 have been either one of the forms already described under this genus, or else one 

 undescribed, but still embraced within its limits. There were two sets of bodies, 

 the one motile the other at rest. The motile forms (Fig, 5, pi. 3) were globular or 

 pyriform, and generally contained a large, roundish, green, distinct mass. They were 

 of course provided with cilia, although at that time I was not able to demonstrate 

 their presence. These bodies, even when moving, appeared to have a distinct 

 wall. After a time they settled down and assumed the quiescent state. The 

 outer coat now rapidly enlarged so as to leave a considerable space between it and 

 the green endochrome, which rapidly underwent division, forming two or more 

 new cells which were still surrounded by the enlarged maternal coat. The num- 

 ber of daughter-cells enclosed in the parent cell varied. A considerable quantity 

 of the water was allowed to stand in a glass jar, exposed to the light. In a very 

 few days all the motile forms had disappeared. The contents of the vessel wore 

 allowed slowly to evaporate. The jar being tall and narrow it was some weeks now 

 before this process was completed, before which consummation hcvmaiococcus forms 

 were abundantly developed. 



Instead of being green, and surrounded by a distant, almost sac-like wall, the cells 

 had acquired a dark brownish-red color, were very opaque, and were protected by 

 a thick wall, whose surface was quite rough. Unfortunately, I did not measure 

 either the active gonidia or their progeny, the quiet cells, but I found the general 



