INFLUENCE OF EXTERNAL STIMULI. LIGHT 



253 



page 1 02 that the anisophylly is here very peculiar and of different 

 strength on shoots of different orders. The lateral shoots of the last 

 order, which are mostly flattened and provided with only four rows 

 of leaves, do not generally shoot out in darkness : although this takes 

 place in the case of the relative chief axis which is equally strongly 

 dorsiventral and anisophyllous. On the shoot which is represented 

 in Fig. 125, for example, the lateral leaves had the characteristic 

 keel upon the back, and two leaf-rows were found upon both the 

 upper and the under side, and they were constructed differently one from 

 the other in the manner already described ; the transverse section 

 of the shoot-axis depicted on the left of Fig. 126 shows that upon 

 the illuminated side the leaf-cushion was more pronounced than it was 

 upon the shaded side. The shoots developed in darkness however had 

 entirely lost the anisopkylly ; the leaves were all developed alike, there 

 was no trace of formation of keel on the lateral leaves, there was only 

 a slight flattening of the shoot-axis observable (see the representation on 

 the right in Fig. 1 26) ; the branching of the shoot also no longer took 



FlG. 126. Lycopodium complanatum. Two cross-sections through the same shoot. That on the left from 

 a portion growing in light, that on the right from a portion growing in the dark. 



place in one plane and it no longer formed the leaf-like lateral shoots 

 with limited growth, in short this shoot behaved essentially like an 

 underground rhizome. Dorsiventrality and anisophylly were directly 

 induced by the light. 



In other cases, for instance those of habitual anisophylly described on 

 page 109, the anisophylly is retained even in etiolated shoots, for example, 

 in Goldfussia anisophylla amongst others. In shoots of this species 

 growing erect the anisophylly is modified but not destroyed, and it may 

 originally have been brought about here in relationship to light. 



1 The lateral axes in the plagiotropous shoot-system of many mosses also do not develop in light 

 of feeble intensity. 



