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THE THEORY OF TRANSFORMATIONS 



[CH. 



typical monocotyledon — such as a grass or a hyacinth, for instance 

 — grows continuously from its base, and exhibits no node or " point 

 of arrest." Its sides taper ofE gradually from its broad base to 

 its slender tip, according to some law of decrement specific to 

 the plant; and any alteration in the relative velocities of longi- 

 tudinal and transverse growth will merely make the leaf a little 

 broader or narrower, and will effect no other conspicuous alteration 

 in its contour. But if there once come into existence a node, or 

 "locus of no growth," about which we may assume the growth — 

 which in the hyacinth leaf was longitudinal and transverse— to 

 take place radially and transversely to the radii, then we shall 



Ficr. 359. 



at once see, in the first place, that the sloping and slightly curved 

 sides of the hyacinth leaf suffer a transformation into what we 

 consider a more typical and "leaf-like" shape, the sides of the 

 figure broadening out to a zone of maximum breadth and then 

 drawing inwards to the pointed apex. If we now alter the ratio 

 between the radial and tangential velocities of growth — in other 

 words, if we increase the angles between corresponding radii — 

 we pass successively through the various configurations which 

 the botanist describes as the lanceolate, the ovate, and finally 

 the cordate leaf. These successive changes may to some extent, 

 and in appropriate cases, be traced as the individual leaf grows 



