1905] PEIRCE & RANDOLPH—IRRITABILITY IN ALGAE 325 
plants of any grade of complexity in a laboratory not provided with a 
greenhouse is in securing proper illumination, a difficulty all the 
greater when one realizes that not only is normal growth dependent 
upon adequate illumination, but many of the other phenomena of life 
are greatly influenced by it. As Kiess (8, 9). and VécuriNc (19) 
go far toward proving, the reproductive processes, as well as the 
behavior of the reproductive elements, are profoundly sensitive to 
light. Therefore, in any series of experiments involving irritability— 
that is to say, in every series of experiments on living organisms— 
the illumination must be carefully considered. Not having any green- 
houses connected with our laboratory, our difficulties were increased. 
Furthermore, in our climate, there is a great contrast between the 
light of the rainy and of the bright days in winter, while in spring and 
summer, the direct sunlight is quite too intense for algae except in 
running water or in large bodies of still water. Between too little 
light at a short distance from a window and too much light near it, 
the right illumination is difficult to find. We attempted to attain 
this by placing our culture dishes on glass shelves in a window looking 
southeast, screening the dishes at times of bright sunshine by a sheet 
of white tissue paper pasted across the lower part of the window. 
BEHAVIOR OF THE ZOOSPORES. 
Locomotion.—While motile, the zoospores are evidently sensitive 
to light, moving toward the more strongly illuminated side of a slide, 
°F coming to rest, when possible, on the light side of the dish in which 
they escape. This is a general statement of a result of our observa- 
ton; but, as has been known since STRASBURGER’S classical study 
(18) of the behavior of swarmspores, they move toward light of a 
certain intensity rather than light of greater intensity, turning away 
“OM spots too intensely illuminated toward comparative darkness, 
Just as they turn from comparatively dark spots to more suitably 
illuminated ones. Since there are still no means of accurately 
measuring either the intensity or the quantity of light falling upon 4 
given Spot, it is out of the question to determine what the minimal, 
*pumal, and maximal illuminations are for motile zoospores, for 
their Production, or for the parent plant. We must, therefore, con- 
t ‘ . 
“nt ourselves with reporting such general observations as we were 
able to make. 
