WISCONSIN PHYTOPLANKTON 39 



Dictyocystis Hitchcockii (WoUe) Lagerheim, Nuova Notarisia 5: 226. 1890; 

 W. & G. S. West, Jour, Linn. Soc. Bot. 35: 531. 1903; Brunnthaler in Pascher, 

 Siisswasserfl. Deutschl., Osterr. u. d. Schw. 5, Chlorophyceae 2: 185, fig. 279. 1915. 



Cells small, length about one and three quarters times the breadth, 

 very slightly constricted, sinus a broad very shallow depression, 

 breadth of isthmus nearly equal to that of semicell ; semicells broadly 

 ovate and with semicircular apices. Vertical view circular. Lateral 

 view similar to that of front view. Chloroplast axial, usually but 

 one in a cell, with four vertical parietal lobes and a single central 

 pyrenoid. Cells connected by a single delicate strand that usually 

 arises near the isthmus. Inbedded in a homogeneous gelatinous en- 

 velope. Gelatinous envelope at times with denser acicular gelatinous 

 rays radiating from the walls of the cells. (Facultative planktont.) 



Zygospores unknown. 



Cells 30-35 [x. long with spines, 15-19 ju, without spines ; 20-30 jn 

 broad with spines, 10-12 /* without spines; isthmus 8-10 ju, broad. 

 Colonies up to 120 /x in diameter. 



Bear (r), Beaverdam (r), Clare (r), Pish (r). Horseshoe (rrr), Kitten (rr), 

 Lae Court Oreilles (ss), Pokegama (rrr). Reserve (s), Eice (rr). Bound (rr), 

 Whitefish (rrr). Wildcat (rr). 



In the cell shape and the tendency towards an arrangement in 

 series radiating from a common center this alga shows a great simi- 

 larity to the Dictyosphaerium Hitchcockii of Wolle and I believe that 

 the organism described above is the one which he referred to Dicty- 

 osphaerium. 



On the basis of WoUe's description of the chloroplast, "each cell 

 having the chlorophyll radiately gathered around a large central 

 granule", Lagerheim created the genus Dictyocystis since this alga 

 evidently does not belong to Dictyosphaerium. In my opinion the 

 ceU shape is sufSciently like certain other Cosmocladium species 

 [particularly C. constrictum (Archer) Joshua] to justify its removal 

 from Dictyocystis to Cosmocladium. The organization of the colony 

 with strands connecting the cells is a distinct Cosmocladium feature, 

 although in most Cosmocladium species these strands are broad and 

 appear as a double line. The radiating strands found in certain 

 colonies seems to be good evidence that there are scattered pores in 

 the wall of this alga as in other Cosmocladium species, but, unfor- 

 tunately, empty cells were not available for the accurate determination 

 of this point. 



The greatest objection to considering the alga a Desmid is the 

 chloroplast. In all members of the subfamily Placodermae, to which, 

 Cosmocladium belongs, there is a chloroplast in each semicell. In 

 C. Hitchcockii there is but a single chloroplast that extends from 

 pole to pole. In its axial position and four radiation lobes, however, 

 it is similar to the type of chloroplast found in a majority of the 

 species in the closely related genus Cosmarium. 



