PARASITIC PLANTS 349 



and the others, under similar conditions, though they reach what 

 we may term the adult stage, remain somewhat weak and stunted, 

 and produce but few flowers and fruits. 



Most of the plants referred to belong to the order ScrophulariacecB, 

 and among them we may mention the Eyebright {Euphrasia), the 

 Yellow Rattle (Rhinanthus), the Cow-wheat {Melampyrum), and 

 the Lousewort [Pedicular is). They generally appear in large 

 numbers close together, often in such abundance as to determine 

 the general colour of the ground on which they grow, and yet they 

 do"not apparently cause much damage to the grass and other plants 

 which they rob. 



These green parasites are described in various chapters, according 

 to their habitats and their flowering seasons ; so we shall do no 

 more here than to briefly refer to their parasitic habits. 



The Eyebright (p. 274) grows on heaths and downs, where it 

 derives organic food from the roots of the neighbomdng grasses. 

 The Lousewort, too (p. 118), which grows in marshes and moist 

 meadows, is parasitic principally on the roots of grasses, apparently 

 without affecting the latter. The last-named species is a perennial, 

 the roots of which have to find hosts that are capable of supporting 

 it year by year. If the host of the present year should happen to 

 die in the autumn, the suckers that were attached to its roots soon 

 die, and the parasite has to seek a new som'ce of supply. This it 

 does by extending its roots until it reaches a new host, and then 

 producing new suckers. Thus we are able to understand the origin 

 of the long roots so often seen on the Lousewort, and also the reason 

 why these roots never grow downwards into the soil, but always 

 horizontally, just beneath the surface. Further, since the roots 

 extend themselves in search of food at times when the supply is 

 temporarily diminished or stopped, it is clear that some reserve is 

 necessary for the elongation referred to. Such a reserve exists in the 

 older, thick portion of the perennial root, near the base of the stem. 



In the case of the Cow- wheat (p. 146) no suckers are produced 

 until the lateral branches of the root of the seedling reach a moderate 

 length ; ^but in order to increase the chances of finding a suitable 

 host these branches are developed in large numbers, and extend 

 themselves in all directions. The suckers produced on them chng 

 very firmly to the root-fibres of the host, which they almost com- 

 pletely embrace. 



The suckers of the YeUow Rattle (p. 118) are globular, often 

 nearly one-eighth of an inch in diameter, and partly smTOund the 

 root-fibres of the plants to which they are attached. 



