126 BRITISH PLANTS 
ence of the parasite upon the host may be partial or 
complete : 
(i.) Partial or Hemi-Parasites.—These possess chloro- 
phyll, and so can make carbohydrate for themselves. 
They are generally found attached to the roots of other 
plants, which they tap for water ; but, like other para- 
sites, they take all they can get, and though water is their 
chief need, food may be absorbed as well. The British 
partial parasites, with the exception of Thesium humi- 
fusum (bastard-toadflax), belong to the Natural Order 
Scrophulariacez, and include the following plants, which 
live attached to the roots of grasses by means of haus- 
toria: Huphrasia (eyebright), Rhinanthus (yellow rattle), 
Pedicularis (lousewort), Melampyrum (cow-wheat), and 
Bartsia. All these plants live in wet grass-communities. 
Grass-roots form a turf so thick that no other shallow- 
rooted plant has a chance in competing with them for 
water. Daisies, dandelions, and other plants growing in 
meadows have long roots which penetrate the turf, and 
so they are not really in competition with the grasses. 
These hemi-parasites, however, are shallow-rooted. Being 
forced, then, to compete with the grass-roots, they solve 
the difficulty by constraining their rivals to their service. 
They fix their own roots upon theirs, and tap them for 
water. But that they take something more than water 
is proved by the fact that, in a field where yellow rattle 
is abundant, the grass is poor and sickly, and much of it 
dies before the season when it should be mown for hay. 
(ii.) Total Parasites.—These are devoid of chlorophyll, 
and depend entirely upon their hosts for food. In the 
British flora the following are total parasites among the 
flowering plants : Lathrea (toothwort), Orobanche (broom- 
rape), Cuscuta (dodder). The first two belong to the 
Orobanchacez, a Natural Order which differs very little 
from the Scrophulariacez, in which most of the partial 
parasites are included. 
(1) Lathrea squamaria (Fig. 41)—The toothwort is 
parasitic upon the roots of trees, chiefly poplars, hazels, 
and beeches. Its body consists of a thick, much-branched 
rhizome, closely set with curious fleshy, tooth-like scales, 
of a grey or dusky-purplish colour, overlapping each other 
and arranged in four ranks. Each scale is hollow, en- 
closing an irregular chamber, which is open to the exterior 
