458 Peirce . — Studies of Irritability in Plants. 
quake of April ] 8, I have so far been prevented from carrying cylindrical 
plants of Anthoceros ftisiformis to the fruiting stage. The spores sown 
earliest, on September 14, 1905, were sown on slow clocks, making a com- 
plete revolution only once an hour. These clocks at first ran somewhat 
irregularly, stopping at times, and consequently spoiling my cultures and 
necessitating restarting them. More dependable means of revolving cul- 
tures than cheap clocks I expect to have in the autumn. I will record, 
however, that the sporophytes of this species of Anthoceros began to be 
of visible size about five months after sowing in cultures on the shelf. This 
shows that, though Anthoceros usually holds over from season to season, it 
can fruit during the first season from the spore, provided the rains come 
early enough and the winter is wet and warm enough. Fimbriaria , on 
the other hand, did not reach the reproductive stage in my cultures during 
this season, and probably requires two seasons in which to mature suf- 
ficiently to reproduce itself. Of this last I am by no means certain, 
however, and I shall watch the results of future experiments to determine 
this point. 
Fig. 16 is a drawing of a plant of A. fusiformis nine weeks after sowing 
on a clock revolving the culture once an hour. This plant is drawn from 
above, and though presenting in general a circular outline, it is bilaterally 
rather than radially symmetrical. It is like those plants of Fimbriaria 
previously described which, growing on slow clocks, resemble both the 
shelf plants and those growing on faster clocks. 
It is evident that only those unshaded plants near the centre of even 
small culture dishes, such as I have described, receive an equal amount 
of light from all directions. Only these plants can be expected to be and 
are radially symmetrical. Between the centre and the outer edge of each 
clock-culture the young plants are decreasingly cylindrical, increasingly 
dorsiventral, and those on the edge are of the usual out of door or shelf 
form. Furthermore, it is now especially evident why it is so important that 
spores must be sown sparingly ; the young plants must be as remote and as 
nearly equidistant from each other as possible to avoid shading. Plants 
shaded on one side by a neighbour even near the centre of cultures on the 
quicker clocks are as dorsiventral as plants on the shelves. The results of 
equal illumination on all sides are clear and certain in all cultures of Antho- 
ceros , but it is necessary to notice carefully that the illumination is equal 
for any particular plant under observation. Remote from the centre of 
a clock culture, or shaded by too close neighbours, or even on a slow clock, 
the illumination is not equal on all sides. Anthoceros appears to be less 
sensitive, or it reacts more promptly, than the other Archegoniates used 
in these experiments. This, however, I shall presently discuss. 
As stated in the introduction, I have but begun experimenting on the 
question of the influence of the direction of light upon the form of sea-weeds, 
