108 THE KATE OF GROWTH [ch. 



conditions. Reaumur was the first to shew, and the observation 

 was repeated by Bonnet*, that the rate of growth or development 

 of the chick was dependent on tem.perature, being retarded at 

 temperatures below and somewhat accelerated at temperatures 

 above the normal temperature of incubation, that is to say the 

 temperature of the sitting hen. In the case of plants the fact 

 that growth is greatly affected by temperature is a matter of 

 familiar knowledge; the subject was first carefully studied by 

 Alphonse De Candolle, and his results and those of his followers 

 are discussed in the textbooks of Botany f. 



That variation of temperature constitutes only one factor in determining 

 the rate of growth is admirably illustrated in the case of the Bamboo. It has 

 been stated (by Lock) that in Ceylon the rate of growth of the Bamboo is 

 directly proportional to the humidity of the atmosphere: and again (by 

 Shibata) that in Japan it is directly proportional to the temperature. The 

 two statements have been ingeniously and satisfactorily reconciled by 

 BlackmanJ, who suggests that in Ceylon the temperature-conditions are 

 all that can be desired, but moisture is apt to be deficient: while in Japan 

 there is rain in abundance but the average temperature is somewhat too low. 

 So that in the one country it is the one factor, and in the other country it is 

 the other, which is essentially variable. 



The annexed diagram (Fig. 25), shewing the growth in length 

 of the roots of some common plants during an identical period 

 of forty-eight hours, at temperatures varying from about 14° to 

 37° C, is a sufiicient illustration of the phenomenon. We see that 

 in all cases there is a certain optimum temperature at which the 

 rate of growth is a maximum, and we can also see that on either 

 side of this optimum temperature the acceleration of growth, 

 positive or negative, with increase of temperature is rapid, while 

 at a distance from the optimum it is very slow. From the 

 data given by Sachs and others, we see further that this optimum 

 temperature is very much the same for all the common plants of 

 our own climate which have as yet been studied ; in them it is 



* Reaumur : Uart de faire colore et elever en toufe saison des oiseaux domestiques, 

 foil ixir le moyeii de la chaleur du fumier, Paris, 1749. 



f Cf. (int. al.) de Vries, H., Materiaux pour la connaissance de rinfluence de 

 la temperature sur les plantes, Arch. Neerl. v, 385-401, 1870. Koppen, Warme 

 und Pflanzenwachstum, Bull. Soc. Imp. Nat. Moscou. XLiii, pp. 41-110, 1870. 



X Blackman, F. F., Ann. of Botany, xix, p. 281, 1905. 



