348 BOTANICAL GAZETTE [NOVEMBER 
the intensity of the light falling upon a body of water than by other 
influences, such as unequal distribution of oxygen, étc. 
2. Apparently the germination of the zoospores of sessile algae 
is induced primarily by interference with their locomotion. When 
this is blocked, germination begins; conversely, when nothing prevents 
locomotion, they do not germinate. 
3. The nature of the attachment formed by the germinating 
zoospores of sessile algae is dependent upon the ‘roughness of the 
surface of the object with which they come into contact. Upon 
extremely smooth surfaces—such as the surface of clean water and 
clean wet gelatine—the spores form either only the shortest most 
rudimentary holdfasts or merely rhizoids; whereas, on relatively 
rough surfaces, the holdfasts are large and conform in their lobing 
to the contour of the surface. Furthermore, ordinarily floating algae 
may sometimes be induced to form rhizoids or other organs of attach- 
ment if brought into contact with sufficiently rough surfaces. 
4. The discharge of the spores or gametes of Dictyopteris, Dicty- 
ota, and Cystoseira is strongly influenced by light, the discharge being 
much more rapid within a few hours after exposure to light than 
before or than in continuous darkness. For this reason the 2a 
of the discharge as well as the rate is strongly influenced by light, 
and a periodicity of discharge is established which follows appto® 
imately the periodicity of daylight and darkness. 
5. The spores of the sessile marine algae studied germimit 
better in normally alternating daylight and darkness than in eae 
ous darkness; and subsequent growth and development follow the 
same rule. : 
6. As shown by WINKLER to be the case with Cystosei@ egttc 
we have found that the direction in which the light falls determine | 
the plane of the first division in the germinating spores of ryt 
erica marina, Dictyopteris, and of Dictyota, the new cell wall 
formed at right angles to the incident rays. ae 
7. Similarly, the rhizoids or holdfasts formed by light 
spores ordinarily issue from the daughter cells away from ne jmes 
In darkness the rhizoids arise in all possible directions, SOmeNN” 
even from both cells of a germinating spore. oe 4 
8. The direction of growth of rhizoid and of plantlet 1s determine? 4 
