Ill] ITS CHEMICAL ASPECT 261 



of growth, or only portions of the rest, can be fitted to this simplest 

 of formulae. In a Hfe-time are many ages; and no all-embracing 

 formula covers the infant in the womb, the suckling child, the 

 growing schoolboy, the old man when his work is done. Besides, 

 we need such a formula as a biologist can understand ! One which 

 gives a mere coincidence of numbers may be of little use or none, 

 unless it go some way to depict and explain the modus operandi of 

 growth. As d'Ancona puts it : "II importe d'apphquer des formules 

 qui correspondent non seulement au point de vue geometrique, mais 

 soient representees par des valeurs de signification biologique." 

 A mere curve-diagram is better than an empirical formula; for it 

 gives us at least a picture of the phenomenon, and a qualitative 

 answer to the problem. 



Growth of sunflower-stem. (After Reed and Holland) 



1st diff. 



15-8 



24-4 



33-3 



39-2 



38-4 



31-6 



22-6 



14-4 



8-5 



4-9 



2-8 



The chemical aspect of growth 



As soon as we touch on such matters as the chemical phenomenon 

 of catalysis we are on the threshold of a subject which, if we were 

 able to pursue it, would lead us far into the special domain of 

 physiology ; and there it would be necessary to follow it if we were 

 dealing with growth as a phenomenon in itself, instead of mainly 

 as a help to our study and comprehension of form. The whole 

 question of diet, of overfeeding and underfeeding*, would present 



* For example, A. S. Parker has shewn that mice suckled by rats, and conse- 

 quently much overfed, grow so quickly that in three weeks they reach double their 

 normal weight; but their development is not accelerated; Ann. Appl. Biol, xvi, 

 1929. 



