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 pe, 100.—Thesiwm alpinum. pieneg 
setting up this rela- (kilesernonh IN SECTION. x 
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 
80 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. 
