Ill] OF PARTS OR ORGANS 95 



Trout {Scdnio fario) : pwportionate groivth of various organs. 

 {From Jenkinson's data.) 



106 194-6 192-5 242-5 173-2 165-3 173-4 337-3 287-7 



While it is inequality of growth in different directions that we 

 can most easily comprehend as a phenomenon leading to gradual 

 change of outward form, we shall see in another chapter* that 

 differences of rate at different parts of a longitudinal system, 

 though always in the same direction, also lead to very notable 

 and regular transformations. Of this phenomenon, the difference 

 in rate of longitudinal growth between head and body is a simple 

 case, and the difference which accompanies and results from it in 

 the bodily form of the child and the man is easy to see. A like 

 phenomenon has been studied in much greater detail in the case 

 of plants, by Sachs and certain other botanists, after a method 

 in use by Stephen Hales a hundred and fifty years before f. 



On the growing root of a bean, ten narrow zones were marked 

 off, starting from the apex, each zone a milhmetre in breadth. 

 After twenty-four hours' growth, at a certain constant tempera- 

 ture, the whole marked portion had grown from 10 mm. to 33 mm. 

 in length ; but the individual zones had grown at very unequal 

 rates, as shewn in the annexed tablet. 



* Cf. chap, xvii, p. 739. 



t " ...I marked in the same manner as the Vine, young Honeysuckle shoots, 

 etc. . . . ; and I found in them all a gradual scale of unequal extensions, those parts 

 extending most which were tenderest," Vegetable Staiicks, Exp. cxxili. 



t From Sachs, Textbook of Botany, 1882, p. 820. 



