with every new generation at the time of re- 

 constitution? May not such changes lead to 

 variations? 

 (5 Vernon showed that the degree of ripeness of ova 

 and sperms of sea-urchins influences the size of 

 the larvae. Moreover, Weismann believed 

 that a struggle goes on in the germs (germinal 

 selection) between the determinants, the strong- 

 er and better nourished determinants deter- 

 mining the character of the germs, and the 

 zygote (see page 55). 



(6) Webber has shown that when white and yellow 



corn are allowed to cross the white ears will 

 have many yellow grains. This phenomenon 

 is due to the fertilization of the endosperm- 

 nucleus by the second sperm cell (the first one 

 fertilizing the egg cell), with the result that the 

 endosperm is influenced the first year by the 

 yellow germ cell. This phenomenon is called 

 Xenia. (See page 124). 



(7) Hormones or Chalones or Internal Secretions. — 



Certain glands the thyroid, pituitary, thymus, 

 suprarenals, pineal, ovaries and testes, and the 

 pancreas secrete substances that have an impor- 

 tant influence on the character of the organs. 

 Some physiological chemists seem to see in 

 Internal Secretions strong evidences against 

 the inheritance of structural units in the germ. 



The External Causes are: 



(1) General effect of locality. — It is a matter of common 



observation that locality has an important 

 influence on animals and plants with regard to 

 their size, yield, quality, flavor, etc. The factors 

 operating are numerous and complex, partly 

 climatic, partly those relating to soil condi- 

 tions, and partly those relating to food supply. 

 In general it may be said that where condi- 

 tions of life differ there will be corresponding 

 variations. 



(2) Food. — The influence of quality and quantity of 



food has long been recognized by breeders of 

 plants and animals. The influence is seen direct- 

 . ly during the young or growing period. When 

 plants or animals are stunted by reason of un- 

 suitable food or an insufficient amount of suit- 

 so 



