Some Experiments on the Effect of External Stimuli 
on the Sporidia of Puccinia malvacearum (Mont.). 
BY 
WILFRID ROBINSON, B.Sc. (Lond.), 
Platt Botanical Scholar in the University of Manchester. 
With seven Figures in the Text. 
I N certain preliminary experiments in which the sporidia of Puccinia 
malvacearum were germinated near a fragment of hollyhock leaf, it was 
observed that all the germ tubes grew in one direction, and pointed towards 
the leaf fragment. This at first suggested positive chemotropism. More 
critical work, however, revealed the fact that it was an effect produced by 
the unilateral illumination of the sporidia. This led to the investigation 
of the tropic influences affecting the germinating sporidia of Puccinia 
malvacearum . 
De Bary 1 first raised the question as to why the germ tubes of 
parasitic fungi turn towards, and penetrate the tissues of their host-plants. 
Even before the publication of the work of Pfeffer on external stimuli 
de Bary suggested that ‘ physical irritations * or chemical stimuli might 
play a part in these phenomena. Later, as a result of numerous experi- 
ments on the chemotropism of Fungi, Miyoshi 2 concluded that certain 
chemical substances attract the germ tubes of Fungi, whilst others repel 
them. Nordhausen 3 accepted Miyoshi’s results and investigated the biology 
of the penetration of plant tissues by Botrytis and other facultative 
parasites. 
More recently Massee 4 has concluded that the germ tubes of Fungi are 
attracted to their hosts by chemotropic substances secreted by the cell sap. 
In 1906 Fulton 5 repeated many of Miyoshi’s experiments, and concluded 
that in the light of known facts, no simple explanation such as the theory 
1 Vergl. Morph, und Biol. d. Pilze, 1884. 
2 Bot. Zeitung, Bd. lii, p. 1, 1894. 
3 Beitrage zur Biol, parasitarer Pilze. Jahrb. f. wiss. Botanik, 1898. 
4 On the Origin of Parasitism in Fungi. Phil. Trans. Roy. Soc. B., 1904. 
6 Chemotropism of Fungi. Bot. Gazette, 1906. 
[Annals of Botany, Vol. XXVIII. No. CX. April, 1914.] 
