THEORY OF THE DEVELOPMENT OF ORGANISMS 121 



way. The pistachio (Pistazia vera), cultivated in 

 Frankfort, which is destroyed by a temperature 

 lower than 7*5 degrees of frost, will survive 12'5 

 degrees if it has been grafted upon P. terebinthus. 

 Moreover, when it is grown from a seedling, it may 

 reach the age of 150 years; but when it has been 

 grafted upon P. terebinthus its length of life is in- 

 creased to 200 years ; while, grafted on P. lentiscus, 

 it reaches only about 40 years ' (Yochting). 



Vochting's experiments upon beetroot are still 

 more characteristic. ' The stem of a beet plant 

 that bore young buds gave rise to vegetative 

 shoots when it was united with a young, still grow- 

 ing root, but to a blossoming stem when it had 

 been grafted, in spring, upon an old root.' 



Similarly, animal growth is correlative in all its 

 stages. When a muscle becomes unusually large it 

 sets up corresponding correlations of growth in 

 many other parts of the body. The bloodvessels 

 and nerves supplying it become larger, and the 

 increase in the nerves leads to corresponding in- 

 crease in the nerve centres. The tendons of 

 origin and of insertion, and the parts of the skeleton 

 to which these are attached, must react to the in- 

 creased size of the muscle by growing larger ; in 

 fact for all the parts of the animal body the con- 

 clusions which Naegeli and other physiologists 

 drew from plants are applicable. All the different 

 elements of the body are in definite and intimate 

 touch with each other. 



This is shown most beautifully and clearly in the 

 extraordinarily interesting phenomena called di- 



