WISCONSIN PHYTOPLANETON 165 



TQT. ELONGATUM G. M. Smith. PI. 43, Fig. 8. 



Trans. Wis. Acad. Sci., Arts, & Lett. 19' : 636, pi. 12, fig. 3. 1918. 



Colonies of 4 or 8 cells. Cells cylindrical, tapering but little towards 

 the poles. ( Euplanktont) . 



Cells 4-5 n broad, 30-35 /x long. 



Bear (3) (rr). 



The cells of this variety are much longer than those of the typical 

 form. 



Family HYDRODICTYACEAE. 



Cells cylindrical, or flattened and hexagonal to trapezoidal with one, 

 two, or four projections. Coenobia of definite shape ; cylindrical with 

 a large number of cells; or disciform with 2-4-8-16-32-64-128 cells. 

 Cells incapable of division after their formation. Chloroplast single, 

 parietal, laminate to reticulate, frequently filling the entire mature 

 cell ; with one to many pyrenoids. 



Asexual reproduction by the division of contents of any cell to form 

 zoospores that swarm within old cell wall or within a gelatinous vesicle 

 extruded from the cell. Zoospores becoming apposed in the shape of 

 the adult cell when they come to rest. 



Sexual reproduction by isogamous zoogametes which fuse in pairs to 

 form angular resting cells which form colonies on their germination. 



KEY TO THE GENERA. 



Coenobe a hollow cylindrical tube with rounded ends HYDRODICTYON 



Coenobe a flattened disc one cell in thickness. 



Number of cells in coenobe always 2 EUASTBOPSIS 



Number of cells in coenobe 4-8-16-32-64-128, very 



rarely 2 PEDIASTBTTM 



HYDRODICTYON Both 1800. 



Cells macroscopic, oblong-cylindrical with rounded ends; united to 

 form a free-floating, reticulate, saccate coenobium. Meshes of nets 

 3-12 (generally 5-6) sided. Cells coenocytic; chloroplast parietal, 

 reticulate at first, later diffuse; pyrenoids single in very young cells, 

 several hundred in mature cells. 



Asexual reproduction by the division of cell contents into very many 

 biciliate zoospores which swarm about in and become arranged as in 

 the mature coenobe within the old mother cell wall. Liberation of the 

 young coenobe by a gradual gelatinization of the mother cell wall. 



Sexual reproduction by zoogametes which are similar in structure to 



