Ill] OSMOTIC FACTORS IN GROWTH 125 



beyond these limitations ; for the affinity with certain types of 

 chemical reaction is plain, and has been recognised by a great 

 number of physiologists. 



A large part of the phenomenon of growth, both 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 velocity of growth depends in great measure (as we have already 

 seen, p. 113) on the amount of water taken up into the living 

 cells, as well as on the actual amount of chemical metabolism 

 performed by them*. Of the chemical phenomena which result 

 in the actual increase of protoplasm we shall speak presently, but 

 the role of water in growth deserves also a passing word, even in 

 our morphological enquiry. 



It has been shewn by Loeb that in Cerianthus or Tubularia, 

 for instance, the cells in order to grow must be turgescent; and 

 this turgescence is only possible so long as the salt water in w^hich 

 the cells he does not overstep a certain Umit of concentration. The 

 limit, in the case of Tubularia, is passed when the salt amounts 

 to about 5-4 per cent. Sea-water contains some 3-0 to 3-5 p.c. 

 of salts ; but it is when the sahnity falls much below this normal, 

 to about 2-2 p.c.^ that Tubularia exhibits its maximal turgescence^ 

 and maximal growth. A further dilution is said to act as a poison 

 to the animal. Loeb has also shewn f that in certain eggs (e.g. 

 those of the little fish Fundulus) an increasing concentration of 

 the sea-water (leading to a diminishing "water-content" of the 

 egg) retards the rate of segmentation and at length renders 

 segmentation impossible; though nuclear division, by the way, 

 goes on for some time longer. 



Among many other observations of the same kind, those of 

 Bialaszewicz t , on the early growth of the frog, are notable. 

 He shews that the growth of the embryo while still within the 



* Cf. Loeb, Untcr.tuchungen zur physiol. Morphologie der Thiere, 1892; also 

 Experiments on Cleavage, J. of Morph. vn, p. 253, 1892; Zusammenstellung der 

 Ergebnisse einiger Arbeiten iiber die Dynamik des thierischen Wachsthum, Arch, 

 f. Entw. Mech. xv, 1902-3, p. 669 : Davenport, On the Role of Water in Growth, 

 Bosto7i Soc. N. H. 1897; Ida H. Hyde, Am. J. of Physiol, xn, 1905, p. 241, etc. 



t Pfldger's Archiv, lv, 1893. 



J Beitrage zur Kenntniss der Wachstumsvorgange bei Amphibienembryonen, 

 B^dl. Acad. Sci. de Cracovie, 1908, p. 783 ; cf. Arch. f. Entw. Mech. xxvm, p. 160, 

 1909; xxxiv, p. 489, 1912. 



