204 



CLIMBERS, PARASITES, SAPROPHYTES. 



with short glandular hairs, which probably serve to excrete 

 excess of water absorbed from the roots of the host-plant 

 (usually Hazel), into which the Tooth wort sends parasitic 

 roots. The curious hollow leaves of the Toothwort are often 

 described as traps for insects, which are supposed to be held 

 fast and digested by the glands lining the branching cavity 

 of the leaf, but this is probably a mistake. 



237. Partial Parasites are plants which contain chloro- 

 phyll and have ordinary foliage-leaves, so that they can make 

 at least part of their organic food by photosynthesis, while 

 they draw their supply of water and dissolved salts from a 

 host-plant. When the seed of the 

 Mistletoe (whose sticky fruits are 

 carried by the birds) germinates on 

 the branch of a suitable tree (Apple, 

 Oak, Hawthorn, etc.), the radicle 

 penetrates the host, and the woody 

 tissues of the two plants become 

 continuous (Fig. 64). 



Several members of the Foxglove 

 family (Scrophulariaceae') are partial 

 parasites, their roots being attached 

 to the roots of other plants, chiefly 

 grasses, though (like the mistletoe) 

 the plant has green leaves which 

 carry on photosynthesis. Examples 

 are the Yellow Eattle, Lousewort, 

 Eyebright, Cow- wheat, and Bartsia. 



Most of these plants grow in swampy grass-fields, and where 

 their roots come into contact with the roots of G-rasses, 

 swellings are formed at the ends of the parasite's roots, 

 from which sucking processes grow into the grass-roots. 

 The suckers are formed in spring, and through the summer 

 they absorb food from the living grass-roots ; during this 

 time the swellings contain no starch. In autumn the suckers 

 store up reserve food, derived from the grass-roots. 



Another British partial parasite, which has sucking-roots 

 attached to the roots of G-rasses and of various other plants, 

 is the Bastard Toadflax (Thesium linaphyllum) ; it is not 



Fig. 64. Young Mistletoe Plant, 

 with Twig of Host-plant in 

 Section. 



