EXPLANATION OF THE PLATES. 331 



PLATE III. 



Pediastrum granulatum, Kiitz.* 



Numerous modifications, all derived from one and the 

 same little pool of water, near Freiburg, Figs. 1 — 9 

 represent the reproduction. (See pp. 161, 184, 200, 

 250.) Magnified 400 diameters. 



Fig. 1 . An old disk, in great part emptied by birth of 

 gonidia. The emptying of the cells of this specimen, 

 the first in which I observed the reproduction, took place 

 before my eyes in the order of the letters a to e; this was 

 on a day in autumn, (Nov. 24, 1848,) in the afternoon ; 

 the empty cells not marked had lost their contents before 

 the commencement of the observation, probably in the 

 morning of the same day. Several of the empty cells, 

 (for instance, a, h, c, e,) distinctly exhibit a cross slit, 

 through which the contents have been discharged ; in the 

 rest the emptying has taken place on the opposite side, 

 so that the slit is invisible in this position of the disk. One 

 cell is in the act of discharging the gonidia, these having 

 in part entered into the projecting portion of the hernia- 

 like vesicle formed by the swollen innermost lamella of 

 the mother-cell membrane, in part still remaining in the 

 internal cell-cavity. Three other cells still possess their 

 perfect contents, but in dififerent conditions. Two of 

 them are filled by sixteen extremely closely crowded 

 gonidia, only half of which are visible, as they form a 



* In giving a name to this species I select that determination which 

 seemed least doubtful ; I must observe, however, that several of the species 

 distinguished by Kiitzing probably belong to the same species, so particularly 

 P. Boryatmm, K. ; subulatum, cruciatum, K. ; and also in part P. Selerusa, 

 Auct., namely, with the exclusion of P. Selenwa, Ralfs., (Innare and elegans, 

 Hass.) ; and P. Selenxa, Nag. ; {pertusum, K.) The length of the horns, 

 as also their clavate rounding off, is variable ; punctated condition of the 

 cell-wall, on the contrary, I found constant ; but it is only distinguishable ia 

 full-grown and empty specimens. 



