OTHER METHODS OF OBTAINING FOOD 215 



species. They grow from seed with fair rapidity, the root 

 of the seedling attaining a length of an inch in two or 

 three days. Shortly after penetrating the soil, the main 

 root puts out secondary branches, which make their way 

 parallel to the surface. As they grow chiefly in woods or 

 among herbage, they speedily encounter the roots of other 

 plants, and on contact being made between one of these 



FIG. 103. Thesium alpinum, SHOWING THE SUCKERS ON THE BOOTS. 

 (After Kerner.) 



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

 like body is developed at the point of contact (fig. 103). 

 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. 104). 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 pericycle. They are best spoken of 

 as haustoria, a term which is purely physiological, and 

 carries with it no anatomical significance. 



