DESMIDIUM. 2 



1 1 



spherical form ; this enlarges, and as it increases in size, forces 

 the sides of the cells apart to more than twice the original 

 diameter (fig. 3); when mature the sides separate and the 

 spores are set free. 



I >. QUADRANGl latum, Kg. Plate II. figs. 13, 14. 



Filament quadrangular, varying in breadth from its twist- 

 ing, having two longitudinal waved line-; joints in front view 

 broader than long, with two ^somewhat rounded crenatnres on 

 each lateral margin. End view quadrangular. 



Diameter 5060 ". 



This is a form which prevails in England and on the Con- 

 tinent, but has ii"i yet been found in this country. I insert 

 it from Dr. \V I's contribution in anticipation of yet find- 

 ing it 



I >. \i-i< nium, Breb. Plate II, figs. 6, 7. Plate X LI X, fig. 7. 



- 1 < > i 1 1 t - in front view, quadrangular, broader than long, with 

 two rounded crenatures on each lateral margin, united at the 



outer porti nlj of each end margin by mutual projections, 



thus producing intervening central oval or oblong foramina. 



I h'ameter 25 38 ji. 



Not so frequent a- />. Sivartzii, but it appear- to be widely 

 scatb red from Pennsylvania and New Jersey as far south as 

 Florida, and probably also northward and westward. 



I>. Baileyi, (Aptogonum Baileyi, Ralls). Plate II. figs. 8-12. 



Filaments triangular, twisted as the preceding, joints united 

 l>\ each end of the lateral margins only, excavated between 

 the angles as the preceding form: the lateral margins are 

 straight, nol bicrenate, k characteristic which separates it from 

 the other species. 



Diameter 25 ".. more or less. 



Found frequently in sluggish waters, without being con- 

 fined to any particular State or State.-. 



The process of fruiting is nol unlike that of I). Swartzii, 

 the separated portions of chlorophyl I fig. 8) unite and concen- 

 trate fig. 9 . then enlarge I fig. 10 I, press out the sides to more 

 than twice the diameter of a sterile filament, then break apart 

 and se| the -pores fri 



