ZYGOSPORE. 19 



zygospore with the empty semi-cells or husks still attached. Figs. 

 4, 9, 10, 11, 16, arc zygospores of various species of Closterium. 

 This condition of copulation and developed spores, zygospores, or 

 sporangium* as often termed, is frequent; the next step or (ter- 

 mination is, it' not of rare occurrence, very rarely detected. Dr. 

 de Bary, of ( Jcrmany, enjoyed a favorable opportunity ; he describes 

 the whole process substantially thus Two cells arc drawn together 

 by a conjugal influence which we have no means of detecting] the 

 semi-cells separate. (Plate XXIV, fig. 27 land pour out their con- 

 tents ; those of the one cell unite with those of the other, at first with- 

 out a distinct investment, but soon the mass acquires a membranous 

 envelope (figs. 28, 29), forms a matrix, or sporangium in which are 

 reproduced new plant- possessed of invigorated vitality. The 

 envelope of the matrix or zygospore is primarily thin and smooth, 

 hut by degrees it acquires increased thickness, and in the Cosmarivms, 

 usually a granular, tuberculated (fig. 28), or more frequently a 

 spinous surface (fig. 29); the spines being sometimes simple hut 

 commonly forked at their extremities. The next step so difficult 

 to be traced is the opening of the wall of the zygospore (fig. 29), 

 setting free small spheres of sarcode; as they issue they enlarge 

 and acquire a gelatinous, or thin membranous wall. The wall 

 thicken- and the sphere enlarges (fig. 30), the contents constrict 

 (fig. 31) first in one direction and then transversely to the plane of 

 the first incision (fig. 32); these parts develop and set free two or 

 four new plants in size and form like the mother cell, except in the 

 cytioderm or membrane; this is not granular, hut smooth, and so 

 remains until after the multiplication by division takes place. After 

 the first division, the new semi-cells assume the characteristic 

 granular surface ; the result of this first division is two plants each 

 composed of one granulated and one smooth semi-cell. The second 

 division will make two perfect cells and two whieh retain the one 

 smooth semi-cell ; the third division produce- eight cells, all of 

 which except the original two semi-cells will be of typical form. 



Hofmeister's views are somewhat at variance with those of 

 De Bary in regard to numbers; lie affirms that the contents of the 

 sporangiums of Cosmariums are transformed by repeated binary 

 subdivisions into eight or sixteen cell.-, which assume the original 

 form, but not full size of the parent, before they are set tree by the 

 rupture or diffluence of the wall of the sporangium. 



The sporangiums of Closterium, Staurastrum and of other genera 

 are supposed to germinate in the same manner as Cosmarium. Plate 



