74 PARASITIC PLANTS [CHAP. vn. 



they not show degradations to colourless leaves 

 as they succeed in growing upon their host 

 plants ? There is but one explanation, that 

 parasitism has become hereditary, and the 

 structural degradations produced by it are 

 hereditary also. 



Lastly, it is difficult to realise how epiphytes, 

 parasites, and saprophytes could have arisen by 

 congenital variations without any " necessary 

 fitness or correspondence" to such changed 

 conditions of life. This difficulty is insuper- 

 ably increased when we ask how the pene- 

 trating roots and haustoria could have so 

 arisen, upon which parasites depend for their 

 existence. Though the seeds of parasites 

 germinate in the ground, they soon perish if 

 they find no host to which they can attach 

 themselves. Which, therefore, is the more 

 probable, that they are the results of self- 

 adaptation to a host, the existing degeneracy 

 being an hereditary result ; or that all this 

 arose by congenital variation quite irrespective 

 of any fitness for parasitism, etc. ? l 



1 The latest contribution on the parasitism of the cow-wheat is a 

 paper entitled " Sur le Parasitisme du Melampyrum pratense," par 

 M. L. Gautier, Revue General de Botanique, tome xx. p. 67. 



