THE GREEN ALGAE OF NORTH AMERICA 175 



P. B.-A., No. 159. Cells all reniforrn to cordate, the lobes 

 turned outward, 4-8 //, diam. Fig. 60. Me., Mass., N. Y., 

 N. J., Pa., Fla. 



The European D. lunatus A. Br. has cells in groups of four ; 

 two intermediate cells ovoid, obtuse ; two lateral cells lunate ; 

 there is no certain record of its occurrence here, but it is to be 



expected. 



21. DICTYOCYSTIS L,agerheim, 1890, p. 5. 



Cells in series on gelatinous branching threads radiating 

 from a central point ; chrotnatophore star-shaped, with one pyre- 

 noid. 



D. HITCHCOCKII (Wolle) I,agerheim, 1890, p. 5 ; Dictyosphae- 

 rium Hitchcockii Wolle, 1885, p. 126; 1887, p. 186, PI. CLVII, 

 fig. 12. Cells 9-13X15-20 /x, ovoid, the longest dimension in 

 the line of radiation. Fig. 61. N. J. 



Removed from Dictyosphaerium on account of the stellate 

 chrornatophore, and the cells arranged along the gelatinous 

 filaments, not merely at their ends. 



Family 5, HYDRODICTYACEAE. 



Cells multinucleate, with net-shaped chromatophore, with one 

 or more pyrenoids ; united in families of definite form ; asexual 

 reproduction by biciliate zoospores, uniting to form a family 

 either in the mother cell, or in a gelatinous vesicle issuing from 

 it ; sexual reproduction by gametes escaping from the mother 

 cell, and by copulation forming a resting zygote, from which, 

 by various intermediate stages, the normal vegetative form is 

 produced. Fresh water plants. 



KEY TO THE GENERA OF HYDRODICTYACEAE. 



i. Colonies net-shape. i. HYDRODICTYON. 



i. Colonies disk-shape. 2. PEDIASTRUM. 



i. HYDRODICTYON Roth, 1800, p. 531. 



Colonies unattached, composed of very many cylindrical mul- 

 tinucleate cells united at the ends by three, rarely by two or 

 four, to form a cylindrical, wide-meshed net with closed ends ; 

 cells all alike ; asexual reproduction by zoospores, formed in 

 great numbers in a cell, finally arranging themselves in a mi- 

 nute net, which is freed by the breaking up of the mother cell ; 

 sexual reproduction by zoogametes formed in still larger num- 

 bers in a cell, and escaping by an opening, either conjugating 

 or developing parthenogenetically ; from the resting spore thus 

 formed come 2-5 large zoospores, developing into irregular 

 angular cells, " polyhedra " in which are developed many small 

 zoospores, uniting to form a new net. Only one species. 



