124 THE RATE OF GROWTH [ch. 



probably, a still better instance of it in the case of Alpine plants *, 

 whose general habit is dwarfed, though their floral organs suffer 

 little or no reduction. The subject, however, has been httle 

 investigated, and great as its theoretic importance would be to 

 us. we must meanwhile leave it alone. 



Osmotic factors in growth. 



The curves of growth which we have now been studying 

 represent phenomena which have at least a two-fold interest, 

 morphological and physiological. To the morphologist, who 

 recognises that form is a "function" of growth, the important 

 facts are mainly these: (1) that the rate of growth is an orderly 

 phenomenon, with general features common to very various 

 organisms, while each particular organism has its own character- 

 istic phenomena, or "specific constants" ; (2) that rate of growth 

 varies with temperature, that is to say with season and with 

 climate, and with various other physical factors, external and 

 internal; (3) that it varies in different parts of the body, and 

 according to various directions or axes ; such variations being 

 definitely correlated with one another, and thus giving rise to 

 the characteristic proportions, or form, of the organism, and to 

 the changes in form which it undergoes in the course of its 

 development. But to the physiologist, the phenomenon suggests 

 many other important considerations, and throws much light on 

 the very nature of growth itself, as a manifestation of chemical 

 and physical energies. 



To be content to shew that a certain rate of growth occurs in 

 a certain organism under certain conditions, or to speak of the 

 phenomenon as a "reaction" of the living organism to its environ- 

 ment or to certain stimuli, would be but an example of that " lack 

 of particularity!" in regard to the actual mechanism of physical 

 cause and effect with which we are apt in biology to be too easily 

 satisfied. But in the case of rate of growth we pass somewhat 



* Cf. for instance, Nageli's classical account of the effect of change of habitat 

 on Alpine and other plants : Sitzungsber. Baier. Akad. Wiss. 1865, pp. 228—284. 



j Cf. Blackman, F. F., Presidential Address m Botany, Brit. Ass. Dublin, 1908. 

 The fact was first enunciated by Baudrimont and St Ange, Recherches sur le 

 developpement du foetus, Mem. Acad. Set. xi, p. 469, 1851. 



