OTHER METHODS OF OBTAINING FOOD 201 



root-branches and a root of a suitable host, a curious sucker- 

 like body is developed at the point of contact (fig. 99). 

 This is a kind of parenchymatous cushion, which partly 

 surrounds the host, and from the inner side of its con- 

 cavity certain absorption-cells grow out and penetrate 

 into the former, pushing their way until they reach the 

 centre of the invaded root (fig. 100). These absorbing 

 organs are often erroneously spoken of as roots. They 

 cannot properly be so 

 called, as they are 

 developed from the 

 cortex of the rootlet, 

 and not, as root- 

 branches are, from 

 the tissue of the peri- 

 cycle. They are best 

 spoken of as haus- 

 toria, a term which is 

 purely physiological, 

 and carries with it no 

 anatomical signifi- 

 cance. 



While the root is 

 setting up this rela- 

 tionship with a host 

 plant, the shoot of the seedling is growing normally. 

 Its leaves and other sub-aerial parts are well developed 

 and discharge their appropriate functions. The plants 

 would not be recognised at all as in any way parasitic 

 without an examination of the subterranean parts. They 

 absorb certain nutritive materials from the roots on which 

 they fix themselves, and generally destroy them. The 

 damage is, however, local, and does not involve the death 

 of the host plant. Indeed, many of these root-parasites do 

 so little harm to the latter that an affected host is often 

 not noticeably different in appearance from a neighbouring 

 plant of the same species which is not attacked. 



FIG. IQQ.Thesium alpinum. PIECE OF A 



BOOT WITH SUCKEB IN SECTION. X 35. 



(After Kerner.) 



