278 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



nical phraseology, anisophylly is a necessary accompaniment of 

 " dorsiventrality." 



The subject of anisophylly (Wiesner, Goebel*) is, however, a 

 very wide one, and no more is intended at this stage than the 

 indication of the fact that all such cases of asymmetry require 

 to be studied from a definitely structural basis;* and that 

 anisophylly is a necessary consequence, both in the form of 

 unequal leaf-members ("Wiesner) and unequal-sided leaves (Goebel), 

 just as in the corresponding case of the formation of the lateral 

 pinnules of a compound leaf. And further, the study of eccentric 

 growth phenomena affords a guide to the type of anisophylly to be 

 expected, that is to say, to the fundamental and primary form 

 of anisophylly, any variations from which must be regarded as 

 secondary specialisations. For example, if the limiting log. spiral 

 curves of a (1-|-1) mesh (fig. 24) be taken as possibly representing 

 a general fundamental symmetrical growth-form for a leaf-lamina, 

 of which asymmetrical homologues would be produced by unequal 

 rates of growth of the general form of the asymmetrical curves 

 used in plotting an asymmetrical construction, the alteration of 

 such a symmetrical form consequent on its development in an 

 eccentric growth-system should be similarly expressed by the 

 curves bounding the quasi-squares of the eccentric system. Such 

 a suggestion, based on the standpoint that the fundamental growth- 

 form of the typical leaf-lamina (the UrUatt of Goethe) is to be 

 derived from a unilateral retarded growth distribution initiated 

 from a basal growth-centre on the surface of the axis, is purely 

 tentative; but the homologues of the log. spiral curves of the 

 centric (5-|-5) system, seen in fig. 96, serve to indicate with 

 sufficient approximation the general fact that the lateral leaf- 

 members of an eccentric growth-system must themselves be 

 asymmetrical, and only those which develop in the plane of 

 eccentricity truly equilateral. The anisophylly, again, is of the 

 general type that the largest side of the leaf is on the side of the 



* Gf. Goebel, Organography of Plants, Eng. trans., p. 99 : " Anisophylly 

 occurs exclusively on plagiotropous shoots and is a character of adaptation which 

 has an evident relation to the directipn of the shoot and especially its position 

 with regard to Ught." 



