No. 551] RELATIONS IN XENOPARASITISM 681 



Cork formed after establishment, 



haustorium through parenchyma, 

 sieve-tubes, and vessels. 



permanent tissues formed after 

 establishment. 



The parallel given above suggests, as intimated in an- 

 other paragraph, that any species which is to become 

 dependent on another species possesses to a large degree 

 the power of adaptability and morphological plasticity, so 

 that the direction of the development of its tissues or 

 organs can to a degree be modified. Atrophies result, and 

 the assumption of unaccustomed functions^ and tissues 

 are organized in harmony with tissue formation, or other 

 physiological activity on the part of the host. 



