GENERAL 155 



Mesocarpus. In such cases the character of the responding mechanism 

 determines the dissimilar modes of response, and hence the latter afford no 

 evidence as to whether the sensory processes are alike or dissimilar in 

 tactic and tropic organisms. 



When the organism or reacting organ places its main axis parallel to 

 the direction of the exciting stimulus we may speak of parallelotropism, in 

 preference to the term orthotropism or to the longitudinal tropism of 

 Frank. Plagiotropism may be used in a general sense, when the main axis 

 is inclined to the direction of the exciting agency. Diatropism was used 

 by Darwin to indicate a tendency to place the main axis at right angles to 

 the orienting stimulus, and is preferable to the 'transversal tropism ' of Frank 

 or the ' homolotropism ' of Noll. The word klinotropism may be employed 

 when the angle between the main axis and the direction of the exciting 

 agency is less than a right angle but greater than zero. The term 

 heliotropism was first used by de Candolle l , while that of geotropism was 

 invented by Frank a . The terms negative and positive heliotropism were 

 introduced by Hofmeister 3 , while various special terms were employed by 

 Darwin, Rothert, and Massart 4 . Curvatures towards the exciting agency 

 may be denoted as positive instead of using the word ' protropic ' suggested 

 by Rothert, or ' anatropic ' as employed by Massart. The reverse curvature 

 will naturally be negative, so that the ' apotropism ' of Darwin, and the 

 ' katatropism ' of Massart are unnecessary. In the same way we may 

 speak of positive and negative klinotropism in preference to 'anaklinotropism' 

 and ' kataklinotropism,' and in certain circumstances the use of the following 

 signs may prevent misconception: f positive parallelotropism, j negative 

 parallelotropism; |-> diatropism ; \/> positive klinotropism, |\^ negative 

 klinotropism. 



A displaced parallelotropic organ returns to its original position either 

 by a positive curvature only (stem) or by a negative curvature only (root), 

 whereas a displaced plagiotropic organ may assume its normal orientation 

 either by a negative or positive curvature according to the direction of 

 displacement. Flattened organs like leaves may assume profile positions, 

 a phenomenon to which the term of paraheliotropism was given by 

 Darwin 5 ; and if the movement involves torsion Czapek speaks of ' stro- 

 phism ' (geostrophism, photostrophism), and Schwendener of ' tortism ' 6 . 



1 A. P. de Candolle, Physiologic des Plantes, a German translation by Roper, 1835, Bd. n, 

 p. 609. 



2 Frank, Die nattirliche wagerechte Richtung, 1870. 



3 Hofmeister, Jahrb. f. wiss. Bot., 1863, Bd. in, p. 86. 



4 Darwin, The Power of Movement in Plants, 1881, p. 4; Rothert, Cohn's Beitrage z. Biologic, 

 1896, Bd. vn, p. 5; Massart, Biol. Centralbl., 1902, Bd. XXII, p. 70. 



5 L-c., p. 357- 



6 Czapek, Jahrb. f. wiss. Bot., 1898, Bd. xxxn, p. 273; Schwendener and Krabbe, 1892, 

 Gesammelte Mittheil., Bd. II, p. 302. [Since the torsion is the result of growth it is difficult to see 



