2oS 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



into two symmetrical halves by but a single plane. Actinomorphic flowers, 

 on the other hand, are symmetrical with reference to any plant passing through 

 the floral axis, being really symmetrical about that axis. The flowers of Epi- 

 lobrium angustifolium are zygomorphic when they develop normally (Fig. 142, 

 at the left). If, however, a flowering shoot with young buds is slowly rotated 

 about a horizontal axis, its own axis being parallel to that of the clinostat, then 

 the flowers that open under these conditions are actinomorphic (Fig. 142, at 

 the right). 



The reasons why gravitation generally produces such different effects upon 

 root and shoot, leading to positive geotropic bending in the one and to negative 

 geotropic bending in the other, are to be sought in the organs themselves; these 



Fig. 141. — Flower of Amaryllis formosissima that has developed under normal conditions 

 (at the left), and another that has developed from the bud in the inverted position (at the 

 right); stamens and pistil are directed downward in both cases. (After Vbchting.) 



organs are internally different and their various tissues are correlated in specific 

 ways in each case. Similarly, the various responses of leaves grown in dark- 

 ness are not due to the external light conditions alone, but must be related to 

 special correlations between leaves and stem. 



As has already been remarked, no insight into the fundamental nature of 

 geotropic phenomena has yet been obtained. The suggestion of certain zoolo- 

 gists that the otocysts of lower animals serve, not as organs of hearing, but as 

 organs of equilibration, has led some botanists 1 to seek such bodies in plants. 



1 Haberlandt, G., Ueber die Perception des geotropischen Reizes. 

 1900. 



Ber. Deutsch. Bot. Ges. 18: 261-272. 



