* 298 The Botanical Gazette. 
plant grows rapidly, and soon becomes large enough to begin 
the formation of another generation of zoospores, which it 
does almost before the main axis has been developed. : 
One of the most interesting and striking peculiarities of the — 
zoopores is their behavior toward light. It has been said © 
that they appear chiefly in the morning, but this is apparently 
due, in part at least, to the change of temperature, for it was 
proved by experiment that they were produced quite s | 
abundantly in a perfectly dark box as in the bright light out — 
side. The effect of the darkness seemed to be to slightly 
tard the time of formation, making its maximum aboutten — 
o'clock in the morning (in winter). The optimum temper 
ture of the water seems to be about 17° C. es 
Like most other zoospores these are heliotropic, swarming 
toward the light in such numbers that the side of the vessel : 
becomes coated with them. Various experiments were pet — 
formed to determine whether this action was really due ®— 
the light or to the heat. The result of these experiments — 
was to show that it is the light rays which influence them, 
though in some cases it seemed that the zoospores at 
slightly affected by the heat. ‘ 
It may be well in closing to state that in 
plants were found whose filaments were trans Ree 
chains of resting spores. These differed little in Dep 4 
pearance from zoospores, excepting that they lacked the Pi 
ment spot and vacuoles, and that their contests " 3 
uniformly distributed in a parietal layer. This ir 
homogeneous and contained several pyrenoids. ie — 
seem to leave the parent cells, but germinate, t ‘ 
ing through their wall. The appearance 
spores suggests that they are modified zoosp 
could any pigment spot be detected or any 0 
such an origin. 
University of Michigan, Ann Arbor. 
aus 
= 
) 
ores, 
tr 
ExpLANATION oF PLATE XXXII. third “a 
All reduced on°" 
Fig. 1. Mature zoospores.—Fig. 2. Filament, showing Sand daring 
of escaping. —Figs. 3, 4. Two cells showing pear) Cluster ¢ 
of zoospores. v, vacuole. 7, pigment spot.—Fi8- 6-11, 
Figures 1-8 X 1150, Figures 9-11 X 859. 
graving 
oe Figs. 
showing characteristic grouping as their motion ceases. 
growth of young plant from zoospore. 
