1905] PEIRCE & RANDOLPH—IRRITABILITY IN ALGAE 333 
218 spores. The first three of these dishes I then set on the window 
shelf, putting into each the same pieces of Dictyopteris that had been 
inthem. The other three I set back in the dark, putting into them 
the same branches which they had previously contained. All the 
dishes had fresh sea-water put into them. At 5 o’clock that afternoon 
so many spores had come out in the dishes in the light that I removed 
the pieces of Dictyopteris from all six and left them undisturbed 
until November 14 in the morning. Then I counted the spores, 
practically if not quite all of which had become fastened to the 
bottom of the dishes. There were now in the dishes in the light 1565, 
2046, and 2245 spores; in the dishes in the dark 866, 1716, and 596 
spores. In the dishes put into the light after darkness there were 
now 5856 spores where there had been only 480 before, a gain of 
5376 or 11.2 times as many. In the dishes kept in the dark there 
Were now 3178 spores, a gain of 2606 or 4.5 times as many. Nearly 
two and a half times as many, therefore, had come out in the light as 
in darkness in the same length of time. 
The counting of such large numbers of small spores, especially 
where they lie very close together, is not easy. To facilitate counting 
and to bring the count to an approach to accuracy, I ruled lines 
about 2.5™™ apart with India ink on the bottoms of the dishes. The 
counting was done over a white surface with a hand-lens magnifying 
about fourteen times. 
To ascertain whether the amount of light has any effect on the 
discharge of spores, I put fruiting branches of Dictyopteris in dishes 
in the dark, in the full diffused light on the window shelf, and under 
black hoods which had a vertical slit on one side about 3™™ wide and 
ty" long. I did not count the spores, but it was evident that most 
had escaped in the dishes in full light, fewest in the dishes in the 
dark, and a quantity between these two in the diminished light. 
: Similar experiments with Dictyota dichotoma yielded results 
Similar in every respect. 
= indicating the relation of light to the process of extrusion of 
_. I may report some of my experiments on Cystoseira. On 
i 8, at 11 o'clock, I put fruiting branches of Cystoseira 
ac: 5 four small dishes, two of which I set in the dark, two on 
y a window, taking pains to have as nearly as possible equal 
