1905] PEIRCE & RANDOLPH—IRRITABILITY IN ALGAE 337 
spores occurs within a few hours after the fruiting material has been 
put into the light after being in darkness, it may be objected that 
there is not time for sufficient growth to take place to develop the 
necessary mechanical pressure, if mechanical pressure has anything 
to do with the matter in such plants as Dictyopteris. In reply to 
this possible objection, I may say that, though the spores are rapidly 
discharged within a few hours, there was no evident increase in the 
accumulation of spores in my dishes until at least two hours had 
elapsed after they were put in the light. There is therefore time for 
owth 
To make this point clear I will report one experiment. Three 
small dishes of fresh fruiting Dictyopteris branches were kept in the 
dark for twenty-two hours. Early in the morning, the material was 
removed from these dishes, in which a considerable number of spores 
had been discharged, and placed in three clean dishes of fresh sea- 
water on the window shelf in the light. From these dishes the fruiting 
branches were removed after the lapse of one hour and put in another 
set of three dishes, the first set being left otherwise undisturbed to 
allow the spores which had escaped to settle and become attached. 
The same was done at the end of each of the two hours following. 
At the end of another hour and forty minutes, I repeated the process, 
and again after the lapse of two hours more. I therefore had five 
sets of three dishes each, in which spores had escaped. The number 
of spores at the time of exposure to light are as follows: 
After 1 hour’s exposure tolight . . . . . . . 36 spores in 3 dishes 
“ 2 hours’ “ “ e 26 a 3 y 
. eg 6“ “ : ee eee 17° “ 3 “ 
. : “ ‘“ “ ee a “ 3 “ 
‘ ¢ a ee 597 “ 3 6“ 
be number of spores in rs dishes . . . . . « 2500 
bia number of spores in escaped last 3% hours . . 2268 
— of spores escaped in last 33 hours . . . 90 
Teentage total time in which these spores escaped. 55 
a these figures it is clear that the discharge of the spores in 
— 1S not an immediate one, but that a certain length of time 
aay “el after the plants are brought into light after darkness 
tak es discharge their spores rapidly. What changes 
© Place under illumination which result in the discharge of the 
