1923] 



MOORE AND CARTER — ALGAE FROM NORTH DAKOTA LAKES 407 



Intercalary cell division is apparently the rule, although growth 

 at the apex is sometimes just as frequent. The cells seem to have 

 a distinct membrane and are embedded in a thick gelatinous 

 sheath of uniform width. There is a definite central body, 

 probably a pyrenoid, which is distinctly visible even in material 

 which has been preserved for some time in formalin (pi. 21, fig. 7). 



Branches can apparently arise anywhere by the expulsion from 

 the sheath of one of the intercalary cells, which then acquires a 

 sheath of its own, and, by rapid and repeated division, may soon 

 outstrip in length the filament which gave it origin (pi. 21, fig. 8). 

 Although a branch thus formed often projects at right angles to 

 the supporting branch, it may arise at almost any angle. Whilst 

 branching by this kind of intercalary proliferation is most fre- 

 quent, there is some evidence that branching at the apex of the 

 filaments may also sometimes occur, although the exact method 

 by which this is performed is not altogether clear. Sometimes a 

 single cell with its individual sheath is seen projecting at right 

 angles to the apical cell of a filament (pi. 21, fig. 8). How such a 

 cell came to occupy this position is not apparent, but it is easy to 

 see how it might, by repeated cell-division, give rise to one of 

 those perpendicular branches so commonly encountered. 



The alga has only previously been known from central Europe. 



Class HETEROKONTAE 



Order CONFERVALES 

 Family Confervaceae 



Genus conferva Linn. 



Conferva bombycina Ag. forma tenuis (Hazen) Collins. 

 Slough below Wheeler's Pond. 



Class CHLOROPHYCEAE 



Order CONJUGALES 



Family Desmidiaceae 

 Genus closterium Nitzsch. 



Closterium Dianae Ehrenb. 



Outer margin 120-140° of arc; length 190-220 y; breadth 18 [&. 



