ELECTROTROPISM. CHEMOTROPISM 481 



electrotropism in Phycomyces ; hence it is preferable to await the accumulation 

 of further data. 



More comprehensive investigations are forthcoming as to the influence of 

 electric currents than as to that of electric radiations. Elfving was the first 

 (1882) to observe curvatures in the root when galvanic currents were sent 

 through the water in which the roots were bathed. These curvatures were some- 

 times positive, the root apex curving towards the positive pole, sometimes they 

 were negative. According to Elfving's statements the direction of curvature 

 depends in the first instance on the nature of the plant, according to Brunchorst 

 (1884) it depends on the strength of the current. A strong current induces 

 positive, a weak current negative curvature, while medium currents produce no 

 effect at all. The medium current is not the same, however, for every plant. At 

 first sight the results obtained in this relation appear to exhibit a certain like- 

 ness to the variation in the heliotropic response induced by different intensities of 

 light. The likeness is, however, superficial since, as Brunchorst has shown, the 

 positive galvanotropic curvatures are generally not phenomena of stimulation, 

 but originate entirely from the fact that growth on the positive side of the root 

 is injured by the current. Probably certain chemical changes are induced by the 

 current which operate first of all inhibitively to growth and finally fatally ; at all 

 events a root which exhibits positive curvature of this character, always dies, 

 not only on that side but altogether, at the latest after 24 hours. The negative 

 curvatures on the other hand appear to be genuine phenomena of stimulation, 

 where the root apex acts as the organ of perception. We have even less ground 

 for assuming that the plant has the power of appreciating electric waves them- 

 selves than we had for believing in its power of perceiving light and heat waves ; 

 in all probability the action of the current is to develop certain bodies by electro- 

 lysis, which lead to appreciation of the stimulus (compare Lecture XLIII). 



The unequal distribution of certain soluble substances may also bring about 

 directive movements. These have been termed chemotropic movements and 

 are especially well seen in Fungi and in pollen-tubes. Miyoshi (1894 a) has 

 confirmed this in the case of certain Mucorinae and in Penicillium, Aspergillus, 

 and Saprolegnia, the occurrence of movements in which was recognized long 

 before and which can be interpreted only as cases of chemotropism. Thus Kihl- 

 MANN (1883) found that the cells of Isaria became bent out of their previous 

 path of growth when placed in the neighbourhood of germinating spores of Me- 

 lanospora parasitica and ultimately grew over them, and De Bary (1884, 393) 

 has suggested that the entry of parasitic Fungi into their host-plants is due 

 to stimuli of a chemical nature. From Miyoshi' s investigations there can be 

 no doubt that chemotropic movements are widely distributed amongst Fungi and 

 generally speaking serve the purpose of guiding the fungus to a suitable nutritive 

 substratum, although chemotropic attraction is also effected by substances 

 which are not good nutrients. Miyoshi advanced further proof of chemotropism 

 by injecting leaves, such as those of Tradescantia, with certain experimental 

 solutions, and sowing spores of a fungus on the moistened epidermis. The in- 

 jection diffused out through the stomata, and, if it was positively chemotropic, he 

 found that the hyphae curved into the stomata, while they grew beyond them 

 when the leaf was injected with water only. Miyoshi obtained similar results 

 by sowing the spores on finely perforated plates of mica smeared over with 

 a chemotropic layer of gelatine. Finally he employed fine capillary tubes filled 

 with the solution, the ends of which he inserted into the drop of fluid of an 

 ordinary slide culture, thus permitting of a diffusion of the stimulating agent. 

 Whenever a straight fungus hypha encountered dissimilar concentrations of the 

 stimulant on different sides, its growing apex bent round until the new growth 

 had placed itself parallel with the diffusion flow of greater concentration, towards 

 which it grew. Wortmann's experiments on the thermotropic curvatures of 

 roots (p. 479) present us with quite similar phenomena, for we may well com- 

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