Ill] OF OSMOTIC FACTORS IN GROWTH 243 



such variations being harmoniously "graded," or related to one 

 another by a "principle of continuity," so giving rise to the 

 characteristic form and dimensions of the organism and to the 

 changes of form which it exhibits in the course of its development. 

 To the physiologist the phenomenon of growth suggests many other 

 considerations, and especially the relation of growth itself to chemical 

 and physical forces and 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 stimuh, would be but an example of that "lack 

 of particularity" with which we are apt to be all too easily satisfied. 

 But in the case of growth we pass some little way beyond these 

 limitations: to this extent, that an affinity with certain types of 

 chemical and physical reaction has been recognised by a great number 

 of physiologists*. 



A large part of the phenomenon of growth, in animals and still 

 more conspicuously in plants, is associated with "turgor," that is 

 to say, is dependent on osmotic conditions. In other words, the 

 rate of growth depends (as we have already seen) as much or more 

 on the amount of water taken up into the living cells f, as on the 

 actual amount of chemical metabohsm performed by them; and 

 sometimes, as in certain insect-larvae, we can even distinguish 

 between tissues which grow by increase of cell-size, the result 'of 

 imbibition, and others which grow by multiplication of their 

 constituent cells |. Of the chemical phenomena which result in the 



* Cf. F. F. Blackman, Presidential Address in Botany, Brit. Assoc, Dublin, 

 1908. The idea was first enunciated by Baudrimont and St Ange, Recherches sur 

 le developpement du foetus, Mem. Acad. Sci. xi, p. 469, 1851. 



t Cf. J. Loeb, Untersuckungen zur physiologischen Morphologie der Tiere, 1892; 

 also Experiments on cleavage, Journ. Morphology, vii, p. 253, 1892; Ueber die 

 Dynamik des tierischen Wachstums, Arch. f. Entw. Mech. xv, p. 669, 1902-3; 

 Davenport, On the role of water in growth, Boston Soc. N.H. 1897; Ida H. Hyde 

 in Amer. Journ. Physiology, xii, p. 241, 1905; Bottazzi, Osmotischer Druck und 

 elektrische Leitungsfahigkeit der Fliissigkeiten der Organismen, in Asher-Spiro's 

 Ergebnisse der Physiologic, vn, pp. 160-402, 1908; H. A. Murray in Journ. Gener. 

 Physiology, ix, p. 1, 1925; J. Gray, The role of water in the evolution of the 

 terrestrial vertebrates, Journ. Exper. Biology, vi, pp. 26-31, 1928; and A. N. J. Heyn, 

 Physiology of cell-elongation, Botan. Review, vi, pp. 515-574, 1940. 



X Cf. C. A. Berger, Carnegie Inst, of Washington, Contributions to Embryology, 

 xxvu, 1938. 



