148 



DYNAMICS OF LIVING MATTER 



FIG. 33. 



each cell of the tip of the stem (Fig. 32). If, however, the stem is put 

 into a horizontal position, these heavier particles will go to the peripheral 

 side of the cells on the lower half of the tip and to the central side of 

 the cells on the upper half of the tip (Fig. 33). This difference in the 



position of these solid particles 

 may determine differences in the 

 reaction velocity of the chemical 

 processes in both groups of cells. 

 In the cells on the upper side 

 the heavier elements are in more 

 direct contact with the substances 

 diffusing into the cells from the 



o 



pith, while in the cells on the under side the reverse is true. These 

 assumptions are purely speculative, serving only as an illustration of 

 the statement that a change in the position of an organ might influence 

 the reaction velocity on the upper and lower sides of the organ differ- 

 ently. In consequence of such an influence, a curvature like that in 

 heliotropic reactions might be produced. 



Czapek has found chemical differences between the tips of roots 

 which were put into a horizontal position and those left in their normal 

 vertical position. In the extreme tips of the positively geotropic roots 

 of Lupinus albus the amount of homogentisinic acid increased about 

 15 per cent in about half an hour when put into a horizontal position. 

 At the same time, a retardation in the blueing of tincture of guaiacum 

 was noticeable, which he considered the effect of the formation of an 

 antioxidase.* It is, however, questionable, whether these chemical 

 changes are responsible for the geotropic curvature. In order to prove 

 this it would be necessary to show a chemical difference in the lower 

 and upper sides of a root or stem which had been put or brought into 

 a horizontal condition. Czapek, however, states that he could not 

 find any difference between the upper and lower sides. 



Animals also show geotropic phenomena, f Antennularia, a Hy- 

 droid, behaves toward gravitation like a geotropic plant, and it would 

 be possible to demonstrate the principle of geotropic curvatures in this 

 animal. When the stem of Antennularia antennina, which normally 

 grows vertically upward, is put into an oblique position in the aqua- 

 rium, the tip bends until it is again in a vertical position, and then con- 

 tinues to grow in this direction vertically upward. The roots are not 

 quite so straight as the main stem, and although thev have a tendency 



* Czapek, Ber. der dentsch. bot. Gesell., Vol. 2O, p. 464, 1902. He obtained similar 

 results in a case of light effects ; ibid., Vol. 21, p. 243, 1903. 



f Loeb, Sitzungsber. der physik. med. Gesellsc/t., Wiirzburg, J anu ary, 1888; and 

 P/Ziiger's Archiv, Vol. 49, p. 175, 1891. 



