VOLUME XL NUMBER 5 
MOTANICAL (AZEPPE 
NOVEMBER, 1905 
STUDIES OF IRRITABILITY IN ALGAE. 
GEORGE J. PErrRceE and FLrora A. RANDOLPH. 
(WITH TWENTY-SEVEN FIGURES) 
INTRODUCTION. 
IN a recent book on the physiology of plants (13) the statement is 
made that “when zoospores and other motile and floating spores of 
sessile plants come to rest, attaching themselves to the substratum, 
the attachment is effected through means not yet wholly clear. . - - 
It remains for experiment actually to show that the increased rate 
and the changed direction of growth in such cases among plants are due 
to contact, though it seems to be the case in animals” (10). 
It was with a view to adding somewhat to our knowledge in this 
direction that the studies here reported were undertaken, first with 
fresh-water algae, and subsequently with marine. We worked 
together on the fresh-water algae; one of us worked alone on the 
sta-weeds;' we have gone over all the results together. 
For the sake of clearness, we may briefly describe the series of 
‘Woes a small part of which we wish to report in some detail. Zoo- 
ae id of Oedogonium, Vaucheria, and other fresh-water algae, after 
scaping from the cells in which they form, may swim about for a 
ensiderable length of time. If they are in the light, the direction of 
: * locomotion is influenced by the direction and intensity of the 
sht which falls upon them. This has long been known, though 
ing, a ahanigeny to express my appreciation of the opportunity ] png 
Zoological a ni - aoe 1904, at one of the posers sar ee 
heartily to ik a: = es by the Carnegie gt ay: : — ik the 
ire cers of the Zoological Station for the y 
321 
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