88 THE CONTROL OF LIFE 



are not interfered with. The full inheritance may not 

 be expressed, but a large proportion of it is realised as 

 usual. What, then, is the importance of nurture ? 



Admitting all this and more, we return to our proposi- 

 tion that the fullness of the development depends in 

 part on the adequacy of the nurture. It is a subject 

 for inquiry in each particular case whether a deficiency 

 in development is due to defective ' nature ' or to de- 

 fective ' nurture.' In any environment, Man will develop 

 two sets of teeth, yet the development of the teeth will 

 in part depend on the nutrition. Very suggestive are 

 certain experiments made by Gudernatch on tadpoles 

 (Amer, Journ. Anat, XV, 1914, pp. 431-478, 2 pis.). 

 Tadpoles fed on minced thyroid showed the usual division 

 of labour and complexity of parts, but they remained 

 small. They became eerie dwarfs, showing difierentia- 

 tion without growth. But tadpoles fed on minced 

 thymus and spleen grew big without growing complex- 

 They showed growth without differentiation. They 

 remained big tadpoles — children that could not grow up. 



Another diagrammatic illustration concerns the red 

 Chinese primrose (Primula sinensis rubra) y so familiar 

 in greenhouses. Reared at 15°-20° C. it has red flowers ; 

 reared at 30°-35° C, with moisture and shade, the same 

 plants have pure white flowers. The development, so 

 far as colour goes, depends on the nurture. The white 

 Chinese primrose (Primula sinensis alba) bears only 

 white flowers whatever be the temperature (see T. H. 

 Morgan and others : The Mechanism of Mendelian 

 Heredity, New York, 1915, p. 38). 



