92 FRESH- WATER ALG^E OF THE UNITED STATES. 



not know any other genus to which it is more closely allied, and do not feel dis- 

 posed to indicate a new one for it. 



Fig. 3, pi. 11, represents a cell-family magnified 250 diameters. 



Genus HYDKODICTYON, ROTH. (1800.) 



Cellulae oblongo-cylindricae, in coenobium reticulato-saccatum connexse, oranes fertiles; alise 

 procreant macrogonidia, quae jam intra cellulam matricalem in coenobiura filiale se connectunt ; aliae 

 microgonidia, quae multo ruinora, cellulae matricalis membranam perrumpunt, polo antico ciliis vibra- 

 toriis binis et puncto rubro laterali praedita sunt, brevi postea in globules protococcoideos tranquillos 

 transformata sporas perdurantes efficiunt. 



Cells oblong-cylindrical, joined into a reticulated saccate coenobium, all fertile; some producing 

 macrogonidia, which join themselves into a coenobium within the parent cell; the others producing 

 microgonidia, which are furnished with two vibratile cilia and a lateral red spot, and which, escaping 

 from the parent cell, are, after a brief period of motile life, transformed into protococcoid thick-walled 

 spores. 



Remarks. The genus Hydrodictyon comprises, as far as known, but a single 

 species, which is common to North America and Europe. It grows in great 

 abundance in the neighborhood of Philadelphia, especially in the ditches and 

 stagnant brick-ponds in the low grounds below the city known as the " Neck." 

 There it very frequently forms floating masses several inches in thickness and 

 many feet in extent, so that with the aid of a rake it could be gathered by the 

 bushel. When thus in mass the color is very generally dingy and yellowish, 

 although the fronds, when in active vegetative life, are mostly of a bright, beauti- 

 ful green. The plant is in greatest profusion in June and July, after which time 

 it gradually disappears, until in the autumn it is scarcely to be found, but early 

 in the spring it reappears. The very young fronds are minute, oval, cylindrical, 

 filmy-looking, closed nets, with the meshes not appreciable to the eye ; when growth 

 takes place, the fronds enlarge until finally they form beautiful cylindrical nets 

 two to six inches in length, with their meshes very distinct and their ends closed. 

 In the bright sunlight they, of course, by virtue of the life-functions of their chlo- 

 rophyl, liberate oxygen, which being set free in the interior of the net, and its 

 exit barred by the fine meshes, collects as a bubble in one end of the cylinder and 

 buoys it up, so that, the heavier end sinking, the net is suspended, as it were, ver- 

 tically in the water. I know of few things of the kind more beautiful than a jar 

 of limpid water with masses of these little nets hanging from the surface like cur- 

 tains of sheen in the bright sunlight. A few cells collected in the fall or early 

 spring, if put into a preserving-jar and the water occasionally changed, will multi- 

 ply, and in a little while become a source of frequent pleasure to the watcher. 



As the fronds increase in size they are always in some way or other broken up, 

 so that, instead of being closed cylinders, they appear as simple open networks of 

 less or greater extent. The extreme length to which the frond attains is, I think, 

 very rarely over twelve inches, with meshes of about a third of an inch in length. 

 The construction of the frond is always the same. It is composed of cylindrical 

 cells united end to end in such a way as to form polygonal, and mostly pentagonal 



