LITERATURE 467 



radicle, flower-bud or sporangiferous hypha — tends to place 

 itself in the axis of the heat rays, if there are any, or to bend 

 towards or from the source of heat. Whether the organ shall 

 bend towards or from the source of heat depends both upon the 

 external temperature and the protoplasm of the plant. The 

 turning is such that it will tend to keep the organ at the opti- 

 mum temperature for its protoplasm, or bring it into such a 

 temperature. The response is thus, on the whole, an advan- 

 tageous one. 



Summary op the Chapter' 



There is in all organisms a close relation between tempera- 

 ture and rate of growth, such that growth is most rapid at that 

 temperature at which the chemical changes of metabolism pro- 

 ceed most quickly. -The position of this optimum varies with 

 the normal thermal environment of the race ; it is attuned, we 

 may say, to that normal temperature. Certain organisms or 

 their parts grow in a definite direction with reference to the 

 source of heat : away from the source when its temperature is 

 too high ; towards the source when the temperature is low. 

 The neutral point varies in the different species in much the 

 same way as the optimum for growth varies. We may say 

 that the different attunements of organisms determine their 

 different neutral points. At the same time these responses are 

 advantageous. In some way the advantageous response of 

 the organism is bound up with its attunement. 



LITERATURE 



AsKENASY, E. '90. Ueber einige Beziehungen zwischen Wachsthum und 



Temperatur. Ber. deut. Bot. Ges. VIII, 61-9i. 23 AprU, 1890. 

 Barthelejiy, a. '84. De Faction de la chaleur sur les phenomenes de 



vegetation. Comp. Rend. CXVIII, 1006, 1007. 21 April, 1884. 

 BiALOBLOCKi, J. '71. Ueber den Einfluss der Bodenwarme auf die Entwick- 



lung einiger Culturpflanzen. Landw. Versuchs-Stat. XIII, 42JU472. 

 CoPELAND, E. B. '96. Ueber den Einfluss von Licht und Temperatur auf 



den Turgor. Inaug. Diss., 59 pp. Halle. Bot. Centralb. LXVIII, 



177-180. 4 Nov. 1896. 

 CuENOT, L. '94. L'influence du milieu sur les animaux. Encyclopedia 



scientifique des Aide-Memoire. Paris: [1894]. 



