DESMIDIFM. 25 



the envelope is diffusing; these unite, end to end, then widen 



and produce a form as fig. 19; fig. 20 is somewhat mure ad- 

 vanced, showing small notches in the sides ; fi:_ r . 21, the begin- 

 ning of the central inflation and the hands ; these continue to 

 develop until the perfect plant is produced. 



Yar. GRACIDESCEN8, Nbrd. 



Wittrock and Nordstedt have, in their series of Alga eossie- 

 oata, No. 367, a -mall variety under tin- name. It i- very 

 small, but the features are those <f the typical plant. It was 

 collected in Brazil. The same -mall form occurs here; have 

 memorandum of it from Long Wood Pond, and Wood Lake 

 of northern New Jersey. 



B. delicati88Ima, Wolle. Plate I. figs. -J--', _';, 24. 



("ell- sub-cylindrical, surrounded in the middle by two 



narrow, thick hand-, twice the diameter of the cylindrical 

 body, cell- four time- a- long as wide. 



Diameter of body, 6-8 ,".: of Land-, 13-17 />. 

 Pond, Pleasant Mill-, New Jersey. 



The characteristic feature- . . t' this plant are the -mall -i/.e, 

 the cylindrical form of the body, the elevation of the bands 

 which surround it, and the elongated proportion of the body. 



Genus, DESMIDIUM, Ag. 



Plate II, figs. 1-14; Plat. III. figs. 1-4. 



Filaments fragile, elongated, triangular or quadrangular, regu- 

 larly twisted, two chlorophyl masses in each cell barely touching 



in the middle. Margiu of cells incised or entire. 



D. cylindricum, Grew [Didymopriivm Grevillii, Kg.) Plate 

 III. figs. 1-4. 

 Cells about half as long as broad, with a thickened border 

 at their junction, medianly more or less deeply incised ; trans- 

 verse view elliptic with the angles somewhat drawn out. 

 Filaments surrounded with a mucous sheath. 



Zygospore spherical, formed by the conjugation of two cells, 

 the chlorophyl passing through a gelatinous connecting tube 

 from one cell to the other (figs. ">. 1 . 



