i8o TROPIC MOVEMENTS 



hypha of Saproleg.nia^ into contact with the oogonium. They probably 

 determine the direction of growth of the fertilizing filaments of Dudresnaya' i , 

 and aid in bringing about the formation and union of the conjugation tubes 

 of Conjugatae 3 . They may also play a more or less important part in 

 determining the union of fungal hyphae to form pseudo-parenchyma or 

 sclerotic tissue, and also in producing and maintaining certain symbiotic 

 associations. 



It is hardly surprising that subaerial organs, such as stems and leaves, 

 should appear usually to be devoid of any chemotropic or osmotropic 

 irritability, for the latter could hardly be of any appreciable use for 

 purposes of orientation in such organs. Roots, however, appear also to 

 have developed these forms of irritability only to a limited extent, for 

 hitherto only a certain aerotropism, or rather oxytropism, as well as a 

 power of curving away from injurious gases, has been observed in them, 

 while they are apparently not subject to chemotropic stimulation by 

 nutrient solutions, or to osmotropic repulsion by concentrated saline 

 solutions. 



After Engelmann 4 had discovered that oxygen exerted a chemotactic action on 

 certain bacteria, Pfeffer 5 studied the phenomenon and showed that a chemotactic 

 irritability was possessed by a variety of freely motile organisms. Stahl 6 then 

 showed the existence of a chemotropic irritability in the plasmodia of Myxomycetes, 

 while Massart 7 established the fact that the repulsion exerted by concentrated solutions 

 independently of their chemical nature was the result of an osmotactic reaction. 

 A variety of researches then followed on the chemotaxis of freely motile animals and 

 plants. Molisch ascribed the curving of the pollen-tube to the stigma to a chemo- 

 tropic reaction 8 and previously examined the aerotropic curvatures of roots 9 . 

 Miyoshi 10 then fully investigated the chemotropic curvatures of fungal hyphae and 

 of pollen-tubes. 



Miyoshi sowed the spores of fungi or pollen-grains on the under-surfaces of 

 leaves which had been injected with water or with nutrient solutions, and then found 



1 De Bary, Beitrage z. Morphol. u. Physiol. d. Pilze, iSSi, 4. Reihe, pp. 85, 90. Cf. Pfeffer, 

 Unters. a. d. hot. List, zu Tubingen, 1884, Bd. I, p. 469; Miyoshi, Bot. Ztg., 1894, p. I. 

 * Berthold, Protoplasmamechanik, 1886, p. 282. 



3 Overton, Ber. d. hot. Ges., 1888, p. 68; Haberlandt, Sitzungsb. d. Wiener Akad., 1890, 

 Bd. XLIX, Abth. i, p. 390. 



4 Engelmann, Bot. Ztg., 1881, p. 440; Pfluger's Archiv f. Physiologic, 1881, Bd. xxv, p. 285 ; 

 1881, Bd. xxvi, p. 541. 



5 Pfeffer, Ber. d. bot. Ges., 1883, p. 524; Unters. a. d. bot. Inst. zu Tubingen, 1884, Bd. I, 

 P- 363 5 1888, Bd. n, p. 582. In the second work (1884, Bd. I, pp. 365, 469) the facts are mentioned 

 which suggested the existence of a power of chemotropic curvature. 



r ' Stahl, Bot. Ztg., 1884, p. 155. 



7 Massart, Archiv d. Biologic, 1889, Bd. IX, p. 515. 



Molisch, Sitzungsb. d. Wiener Akad., 1884, Abth. i, p. in. 



9 Molisch, 1893, Bd. cn, Abth. i, p. 423; a preliminary communication in Sitzungsanzeiger 

 d. Wiener Akad., January 17, 1889. 



10 Miyoshi, Bot. Ztg., 1894, p. i ; Flora, 1894, p. 76. 



