iv ENVIRONMENT AND GROWTH 199 



many other external conditions exert a considerable 

 influence on growth and weight, such as light, heat 

 etc. In 1709 De Vallemont 1 noticed others may 

 have done the same before him that in trees the 

 wood is thicker on the southern than on the northern 

 aspect, and he ascribed this fact to the greater heat 

 received by the southern side of plants ; and Kraus 

 has shown that fruits grow much more during the 

 night than during daytime, the difference being be- 

 tween eighty or ninety and twenty or ten per cent. ; 

 eighty per cent, of the growth of an apple, for instance, 

 occurring at night-time, while twenty per cent, 

 occurs during the day. 2 On these points further 

 information is to be found in any text-book of 

 plant physiology, such as those of Sachs or of 

 Vines. 



Concerning animal growth and its dependence upon 

 external conditions, Yung, 3 of Geneva, has performed 

 many useful experiments, showing how considerable 

 variations are induced in the length and dimensions 

 of tadpoles through the use of different foods, animal 

 foods, such as egg and flesh especially, being much 



Memoires de f Academic Royale des Sciences, 1772, p. 99 of Part I. of 

 the Memoires. 



1 Curiosites de la Nature et de FArt, 1709, p. 57. 



2 Cf. Naudin, Rythme de la Croissance. Revue Horticole, 1872, 

 p. 408. 



3 Cf. his recent Propos Scientifiques^ in which are abstracted most of 

 his investigations. 



