HYAI.OTHECA. 23 



control of .small pools, trenches and outlets of springs. In its 

 younger state it is attached to the muddy bottom, or sticks or 

 stones ; but more commonly it is found in floating masses. 

 The filaments are generally fragile, but sometimes they occur 

 elongated and strong. When gathered in proper season, and 

 kept in water for a few days, the cells separate at the articu- 

 lations, and float in free joints, which being nearly square, 

 readily turn over and present the circular end view, with the 

 stellate arrangement of the chlorophyl. I have had a quantity 

 in good condition for observing the successive stages of conju- 

 gation. The cells separated the same day the collection was 

 made ; and soon thereafter copulation of cells commenced. 

 Plate I, figs. 7, 8, are two floating cells, one in front and the 

 other in transverse view ; they are drawn to each other by 

 some hidden conjugal influence, put forth a mucous tube and 

 unite as fig. 9, then each cell breaks into two ; thus four parts 

 are united ; sometimes all present themselves to view, but 

 more commonly only three are visible, as figs. 10 and 11. The 

 chlorophyl concentrates to the space between the cells ; fig. 

 10, shows an early stage ; fig. 11. a more advanced condition ; 

 and fig. 12, the developed zygospon . Single matured zygo- 

 sjjoresare frequently noticed in gatherings from waters where 

 the plant prevails. 



H. MUCOSA, (Mert) Ealfs. Plate I, fig. 13. 



Filaments scarcely fragile ; joints not constricted, but 

 having at one of the ends a minute bidentate projection, the 

 adjoining end of the next joint being similar. These pro- 

 jections are visible only in older plants. 



Diameter 19-21 /*. 



This plant is not so frequent as the preceding, but it appears 

 to be widely distributed, not in masses, but frequently mingled 

 with other filamentous forms. Had it from ponds of Penn- 

 sylvania, New Jersey, Vermont, Rhode Island, South Carolina 

 and Florida. 



It is easily distinguished from the preceding by its wider 

 mucous sheath, by the straight margin of the cells, by the 

 longer joints and by the central gathering of the chlorophyl. 

 The mucous sheath, being entirely colorless, is not easily dis- 

 cerned, except when surrounded by turbid water. 



H. UNDULATA, Kord. Plate LXIV. 



Cells about twice as long as wide, sides concave and angles 

 rounded, closely connected ; filaments are involved in a 

 wide, colorless, gelatinous sheath. The constriction of the 

 cells, and the rounded angles make an undulate margin. 



Diameter 9-12 p. without sheath. 



