Peirce .■ — Studies of Irritability in Plants . 453 
out of doors. This was due largely to the dry and cold November and 
December, during which out-of-door plants grew but little. 
2. The Influence of Light upon Germination and Early Growth. 
The germination of the spores of various archegoniates has been 
repeatedly described in monographs and in larger works 1 , and the 
development of these plants has been studied by many plant physiologists, 
but I was interested to compare the early stages of germination and 
growth, with reference to the influence of light, with the behaviour of 
germinating algal spores, as described by Rosenvinge, Winkler, and 
myself 2 . To do so, I sowed the spores of A. fusiformis , Fimbriaria 
Californica , and Gymnogramme triangularis, which I had collected when 
ripe during the season of 1905, on white filter-paper over damp soil, in 
covered crystallizing dishes enclosed in black paper. On the side next the 
window I cut a hole 1 centimetre square in the black paper. The sowing 
was on March 29. On April 12 I found the first young plants of A. ftisi- 
formis , two weeks after sowing. These are shown in PI. XXXV, Fig. 1. 
The arrow indicates the direction of light. In this culture the sowing was 
not uniform, and there was more or less shading of adjacent spores by each 
other ; yet, with the apparent but not real exception of the two plants 
a and b , which were shaded (the shading neighbour of a is not shown), 
all were not only growing toward the light, but their first division walls 
were, like those of the algae previously referred to, at right angles to the 
incident rays. We have here, then, photaxis of the germ-tube, and 
the determination of the angle of division by the direction of illumination. 
The influence of light on germination is indicated by the fact that at 
3 centimetres away from the opening in the black paper there were no 
germinations ; at 2*4 centimetres, one ; at 2 centimetres there were ten ; 
at 1-5 centimetres, twenty-five ; and from there on there were too many to 
count. From this statement, and from Fig. 1, we see, in the first place, 
that germination itself is dependent upon a certain though undetermined 
amount of light ; and, in the second place, that the direction of growth, and 
of the successive cell divisions, is determined by the direction of light. 
Fig. 2 represents a Fimbriaria spore germinating thirteen days after 
sowing, the arrow, as before, indicating the direction of the incident light. 
This figure shows that the direction of growth of the germ-tube and of the 
first division walls is determined by the direction of the light. It may be 
objected that the division walls are laid down at right angles to the long 
axis of the germ-tube, and not at right angles to the incident rays. This 
1 For example Campbell, D. H., Mosses and Ferns, 2nd edition, 1905. 
2 Rosenvinge, L. K., Influence d’agents exterieurs sur l’organisation polaire et dorsiventrale 
des plantes, Revue gen^r. de Bot., i, 1889. Winkler, H., Einfluss ausserer Factoren auf die 
Theilung der Eier von Cystoseira barbata, Ber. d. Deutsch. Bot, Ges., xviii, 1900. Peirce and 
Randolph, loe, cit, 
H h 2 
