114 THE EATE OF GROWTH [ch. 



irregular, and sometimes (we might even say) misleading *. The 

 fact also, which we have already learned, that the elongation of a 

 shoot tends to proceed by jerks, rather than smoothly, is another 

 indication that the phenomenon is not purely and simply a 

 chemical one. We have abundant illustrations, however, among 

 animals, in which we may study the temperature coefficient under 

 circumstances where, though the phenomenon is always compli- 

 cated by osmotic factors, true metabolic growth or chemical 

 combination plays a larger role. Thus Mile. Maltaux and Professor 

 Massartf have studied the rate of division in a certain flagellate, 

 Cliilomonas faramoecium, and found the process to take 29 minutes 

 at 15° C, 12 at 25°, and only 5 minutes at 35° C. These velocities 

 are in the ratio of 1 : 2-4 : 5-76, which ratio corresponds precisely 

 to a temperature coefficient of 2-4 for each rise of 10°, or about 

 1*092 for each degree centigrade. 



By means of this principle we may throw light on the apparently 

 comphcated results of many experiments. For instance. Fig. 28 

 is an illustration, which has been often copied, of 0. Hertwig's 

 work on the effect of temperature on the rate of development of 

 the tadpolef , 



From inspection of this diagram, we see that the time taken 

 to attain certain stages of development (denoted by the numbers 

 III-VII) was as follows, at 20° and at 10° C, respectively. 



At 20° At 10° 



That is to say, the time taken to produce a given result at 



* Blackman, F. F., Presidential Address in Botany, Brit. Ass. Dublin, 1908. 



f Rec. de Vljist. Bot. de Bruxelles, vi, 1906. 



X Hertwig, 0., Einfluss der Temperatur auf die Entwicklung von Bana fusca 

 und R. esculenia, Arch. f. mikrosk. Anat. li, p. 319, 1898. Cf. also Bialaszewicz, 

 K., Beitrage z. Kenntniss d. Wachsthumsvorgange bei Amphibienembryonen, 

 Bull. Acad. Sci. de Cracovie, p. 783, 1908 ; Abstr. in Arch. f. Entwicklung smech. 

 xxvm, p. 160, 1909. 



