224 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
and cultures will have to show whether they both can be produced 
from the same mother colony. Until the question is settled it is 
certainly more convenient to keep them under the old names of 
Meyen, Kützing, and Braun. I shall call the type shown in 
FIGURE 14 P. duplex Meyen var. reticulatum Lagerh. (Meyen, 
729, pl. 43. f. 16 and 17; Lagerheim, '82, pl. 2. f. 1), and the 
forms shown in my FIGURES I5-2I, P. clathratum A. Br., P. 
pertusum Kützing, may very well be Braun's var. asperum, 
though there may be a form with smooth spines connecting P. 
asperum with P. Boryanum. This form of mine (FIG. 14) is 
plainly Lagerheim's P. duplex var. reticulatum (82, pl. 2. f. 1). 
P. clathratum A. Br. 
In Pediastrum clathratum A. Br. we have a species of the Diac- 
tinia in which the four-lobed cell type has been carried to its extreme 
development. It is a fairly common and abundant species, ap- 
parently vigorous and well adapted to the conditions it finds. In 
the extreme length of its cell lobes as compared with other species 
of the Diactinia, P. clathratum is obviously a climax type. What 
we may call the body of the cell in P. Boryanum (FIG. 12) has gone 
over almost completely into the four spinous lobes. The cell is 
quite H-shaped, with cross-bars little or no thicker than the arms 
(FIGS. 15-18). As a result, the adaptation of the lobed form of 
the cells to the exigencies of colony formation, with cell numbers 
EA 
МАЛИ 
ue 
Fics. 15 and 16. Pediastrum clathratum A. Br. Sixteen-celled colony and type 
diagram. Fig. 15 X about 300. 
produced by bipartition, works out in quite a different way from 
that in P. Boryanum and P. asperum (пс. 13). It is a type in 
which the four-lobed form in its extreme development has resulted 
in a reduction of stability and compactness in the organization of 
