322 BOTANICAL GAZETTE [NOVEMBER 
even now far from perfectly understood (7). When the zoospores 
come to rest, they surround themselves with a cellulose wall. If they 
come to rest in contact with a solid object, their form changes as 
well; the part against the solid flattens and adheres to it. Thus a 
holdfast is formed. The young plant, now sessile, may pass rapidly 
by successive periods of cell-division and of growth through the 
subsequent stages of its development. The activities of zoospores, 
then, are greatly influenced at different times by various agents; the 
direction of their locomotion is determined by the intensity and direc 
tion of the light falling upon them, the formation of cell-wall imme 
diately follows their coming to rest; the growth of the foot or holdfast 
is proportioned in form and extent to the roughness of the surface 
with which the zoospore is in contact; and the direction of the first 
cell-division is probably determined mainly by the light. ‘These last 
three points we shall discuss in detail. 
Turning for the moment to the behavior of the non-motile spores 
of marine algae, such as those of Fucus, Cystoseira, Dictyopteris 
(Halyseris), we see nearly the same phenomena exhibited. There 
is no independent locomotion, and hence the transport of the spore 
from their points of origin to where they are to germinate is not direc- 
ted by the influence of light upon them, but by water currents. The 
formation of the cellulose wall, the growth of the foot, and the direction 
of the first cell-division (20) are, however, determined by the same 
influences as those controlling the similar phenomena among fresh: 
water algae. These we hope the following pages will make - 
We shall report first upon the fresh water algae, as it was upon 
that we began our work. 
I. FRESH-WATER ALGAE. 
MATERIAL AND METHOD. 
Vigorous plants of Oedogonium, somewhat crowd 
and other low forms, were found in watering-troughs z 
paddock or on pasture in the vicinity of Stanford University; | a 
fornia. Many of the plants were growing attached to the wee 
the troughs, submersed but near the surface of the yes a 
cases fully exposed to the light, in others partly — aj a? | 
Other Oedogonium filaments were found attached to Loe 
ed by diatoms 
for horses 
