1900] CHANGE OF FORM IN GREEN ALGH 393 
invariably changed. In forty-six cultures only three are excep- 
tions to this. The cells at the edge of the original mass elongate 
and become ellipsoidal or even cylindrical, and when division 
occurs it is by means of a wall lying transverse to the long axis 
of the cell (figs. 7, 75, 76). Thus filaments grow out around 
the periphery of the original group. The interior cells do not 
change their form and do not divide further; at length they form 
the center of a mass of long radiating filaments. Branching of 
a cell. occurs by means of a papilla-like lateral outgrowth, which 
Scut off by a wall transverse to its long axis. The walls between 
the filament cells thus formed do not split ; thus there is no 
bulging of the end walls and no separating of the cells. The 
older cells of a filament (for division occurs only at the tip) 
bulge at the sides and become barrel-shaped, but the end walls 
hold them fast together and prevent them forming true spheres 
(ag. 25). It is apparently this coherence of the walls and the 
‘nentation of the walls with reference to the form of the cell 
Which constitutes the filamentous habit. 
‘s the osmotic pressure of the fluid is increased there is a 
“ntinual lessening tendency on the part of the plant to produce 
filaments, and there arise fewer and fewer filaments at the edge 
%: the cluster, Also these filaments tend to go back, by a round- 
Si breaking apart of their cells, into the original form. -The 
see ee of the filaments do this, while the younger ones corsant 
li, © advance by cylindrical cells (figs. 4, 51 10 25: a 34). 
2 y most concentrated solution (pressure 3856 WV x 10 +) there 
ome still five cultures out of ten wherein filaments were formed, 
Fi s but one of these the filaments were only two or — 
a, aaah Back of these cells a thick strand of palmelloi 
: od ed the path of the advancing filament tip (Jigs. am 30). 
»~Hange of the cylindrical cell to a spherical -— aed 
aay * it is, by a corresponding change in the direction of 
in filam 8, will be discussed when we consider the eeee 
— For the present it is enough to note - sme 
Mri pressure the tendency to produce peripheral fila 2 
8, both in the number and in the length they “_ 
