Studies of Irritability in Plants \ 
BY 
GEORGE J. PEIRCE. 
Associate Professor of Plant Physiology in the Leland Stanford Junior University. 
The Formative Influence of Light. 
With Plate XXXV. 
i. Introduction. 
1 my experiments were abruptly terminated by the earthquake of 
April 1 8, it seems on some accounts desirable to record and partly to 
discuss the results I already have, rather than wait until I can report more. 
These experiments have been repeated, most of them many times, always 
with the same results, and I shall go on in the lines which this paper 
suggests as soon as circumstances permit. The statements of fact I make 
with no hesitation ; the interpretation of these facts I offer subject to such 
modification as my further work may make necessary. Yet I cannot help 
feeling that I have gone far enough to justify positive conclusions so far as 
two species of plants are concerned, and to suggest the reasonableness 
of the inference that the conditions are not fundamentally different with 
a considerable number of others. 
In 1898 Czapek 2 reported: ‘ Wenn man Brutkorper von Marchantia 
auf feuchtem Substrat am Lichte . . . auf dem Klinostaten auskeimen 
lasst, so entstehen im Laufe von 2-3 Monaten kleine schwachiiche 
Pflanzchen, welche aus rohrig zusammengeschlossenen Thalluslappen 
bestehen, und rings Wurzeln tragen . . . Dieser interessante Versuch 
1 The first paper in this series — Studies of Irritability in Algae, Botanical Gazette, 40, Nov., 
1905 — was published by Miss Flora A. Randolph and myself. The work of the present paper has 
been done either by myself alone or, under my direction, by two students, Miss Cora A. Snyder and 
Miss Clara A. Tompkins. I assume the responsibility for what I here say, however, for I cannot 
submit this paper to my sometime collaborators, and I have carried the work further than either of 
them knows. I wish also to acknowledge the careful help of Mr. R. M. Holman, now Assistant 
in Botany in this University. 
2 Czapek, F., Weitere Beitrage z. Kenntniss der geotropischen Reizbewegungen. Jahrb. f. w. 
Bot., xxii, 261, 1898. 
[Annals of Botany, Vol. XX. No, LXXX. October, 1906.J 
