FKKS11- WATER ALGJi OF THE UMTK1' STATES. 87 



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

 II.IM In i ii taking place the spore coat has been hi'comini; gelatinous and enlarging, 

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

 furmril (fig. 4/>, pi. 7). So fur, 1 think, is positive. The next step I have never 

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

 4 r, pi. 1) which are of very various sizes and are elliptical, globose, or oval. They 

 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. 



ula- sphirroiileir, aut singnlir, liberto, vesicula chloropbyllosa ct locello lateral! pallidiori cavo? 

 ihstrurta-. limbo livuliuo ct teguuientis uepe smplissimis cincUe, aut plures in stratum vel acervulos 

 cuinuUtte. 



I'ropagatio fit zoogonidiis cytioplasmatis divisione ortis, e cytiodermatis abaviae (intclligc tegu- 

 nirntiiiu extremum) rupturis cxcvdcntibua 



< b spheroidal, either single, free, furnished with a chlorophyllous vesicle and a paler lateral 

 (hollow .'i 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 

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



/,' murk*. But a few weeks after the commencement of my study of fresb- 

 u.it, r :ilir:r, 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 full of what I now know to 

 ha\e been either one of the forms already described under this genus, or else one 

 umleseriheil, 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 

 i>f 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 

 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 were 

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

 before this process was completed, before which consummation hcematococcua 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 



