i68 TROPIC MOVEMENTS 



of the nodes of grasses when the haulm is rotated horizontally so that 

 gravity acts at right angles to the stem and equally on all sides, but does 

 not exercise this action to any appreciable extent when the haulm is rotated 

 in a vertical plane so that it is horizontally inclined only for short periods 

 of time. Similarly when an organ is equally illuminated on all sides, the 

 direction of the light rays is by no means immaterial, since more penetrate 

 when they fall perpendicularly to the surface than when they fall obliquely. 

 Swarm-spores react phototactically in spite of their rapid revolution around 

 their longitudinal axes, and this fact is an indication that a special 

 distribution of irritability may be able to prevent a tropic action being 

 eliminated by revolution on a klinostat. 



Neither Czapek nor Noll l has paid full attention to these considera- 

 tions, for the former concludes that all geotropic action can be eliminated by 

 sufficiently rapid revolution on a klinostat, while both authors often do 

 not sufficiently distinguish between tropic and nastic stimuli and reactions, 

 and ignore the possibility of changes of tone being produced by the 

 transition from diffuse to unilateral stimulation 2 . 



Seedlings should be kept in moist air when used for experiments, and the older 

 adult portions of the root may be covered with wet filter-paper with one end of the strip 

 in water. In order to observe roots or rhizomes in earth or sawdust, they should be 

 grown in wood or zinc troughs with sloping glass sides, and pierced with holes 

 beneath 3 . Cut branches and peduncles may be placed in moist sand heaped up 

 beneath a covered zinc or glass cylinder. 



Any apparatus may be used as a klinostat which is capable of performing 

 regular rotation, but the form prepared by Albrecht of Tubingen under Pfeffer's 

 instructions is extremely exact and serviceable 4 . (Fig. 36.) 



The movement is produced by a strong spring regulated by a fan, the mechanism 

 being attached to the lid (6) of the heavy box (h). One of the three axes on the 

 upper surface of the lid is joined by the gimbal joint to the axis (c), which rotates on 

 the friction-wheels (0), and has a pot attached at (g). The longer axis (m) is used to 

 attach a cylinder (t) containing germinating seedlings (/). If the cylinder contains 



1 Czapek, Jahrb. f. wiss. Bot., 1898, Bd. xxxn, pp. 189, 270; Ber. d. hot. Ges., 1901, 

 Generalvers., p. (129); Noll, Flora, 1893, p. 357; Jahrb. f. wiss. Bot, 1900, Bd. XXXIV, p. 459 

 Ber. d. bot. Ges., 1902, p. 409. 



2 As a matter of fact it is only a question whether the same effect is produced on a klinostat as 

 when the exciting agency acts simultaneously on all sides, and from this point of view the impossi- 

 bility of rigidly separating tropic and nastic reactions is of no importance. Every light ray, and also 

 the most momentary illumination, exerts a stimulating phototropic action, and the absence of 

 a response simply shows that the opposed stimuli balance. Hence, even when a plant is rapidly 

 rotated on a klinostat, it is still subject to phototropic and geotropic stimulation so long as its 

 irritability is unaltered. 



3 Sachs, Arb. d. bot. Inst. in WUrzburg, 1873, Bd. I, p. 387. On a geotropic chamber see 

 Sachs, Flora, 1895, p. 293. 



* See Bot. Ztg., 1887, p. 27. 



