THE PLANT AS A HOST 47 



groups those which are only partially dependent 

 upon their hosts, and those which can in no way 

 support a separate existence. The common wood- 

 land plant, the Cow Wheat (Melampyrum), attaches 

 itself by disks to the surrounding roots of its 

 neighbours, yet this union only occurs in the case 

 of a proportion of the roots. The plant has, 

 too, independent soil roots, and at the same 

 time develops perfectly green leaves. In much 

 the same way the Yellow Rattle (Rhinanthus) of 

 our pastures attaches some of its roots to the 

 underground runners of grass. Yet so green is 

 the foliage, and so abundant the independent 

 roots, that the plant can only draw to a small 

 extent upon the resources of its host. These two 

 species are only types of several hundred plants, 

 existing in various parts of the world, which live 

 partly at the expense of their hosts by means of 

 root attachment. 



There are few more curious plants than the 

 Tooth wort (Lathrcea), a species which is wholly 

 given over to parasitism. Owing to the courtesy 

 of Mr. E. J. Allard, of Cambridge, the writer is 

 able to give an illustration of the Tooth wort. 

 Though not common the plant has a wide dis- 

 tribution, being found on the roots of Poplar, 

 Hazel, and other trees. The Toothwort is very 



