176 CLIMBING PARASITES. GREEN-LEAVED PARASITES. TOOTHWORT. 



throughout the year wherever they have once attacked the host. If the woody 

 branches of the host, with haustoria fastened in them, grow in thickness and 

 superimpose new wood-cells upon the wood, down to which the absorbent cells of 

 the haustoria have penetrated, these suction-cells of the Dodder are likewise inclosed 

 by the wood-cells, and, in proportion to the augmentation of the circumference of 

 the wood in the branch in question, they also lengthen out so that the bundle of 

 absorption-cells proceeding from a sucker may, in such cases, be seen imbedded in 

 the wood to a depth of several annual rings. 



The Cassythse, referred to above, behave exactly like the Dodders. In them 

 also the seedling which issues from the seed is filiform, and lives originally at the 

 expense of reserve-food stored up within the coat of the seed. So, too, it grows 

 upward, ramifies, and endeavours, by means of revolving movements of the apex, 

 to reach a living support, coils round the latter when found, and uses it as a 

 nutrient substratum. Here, again, at the parts where the tendrils of the filiform 

 stem are firmly appressed to the living support, rows of wart-like suckers are 

 developed, and a bundle of absorption-cells gi'ows from each into the host. As in 

 the Dodder, the lower extremity of the filiform stem then dries up at once, and 

 connection with the earth is thus cut off. The parasite, once attached by its 

 haustoria to the host, is able to branch repeatedly, to weave its thread-like stems 

 over all the branches and to climb to the top of the host, even should the latter be 

 a tall bush. At some spots everything is entangled to such an extent that one 

 would think there were birds' nests amongst the boughs. 



The second series of parasitic Phanerogams consists of herbs bearing green 

 foliage-leaves, whilst the seed contains an embryo furnished with seed-leaves 

 (cotyledons) and root. The seeds germinate in the earth and there develop seed- 

 lings without the support of a host; it is branches of the root that first attach 

 themselves by means of suckers upon the roots of other plants. To this series 

 belong about a hundred Santalaceas, mainly of the genus Thesium, and many more 

 than two hundred Rhinanthaceas besides. The chief examples of this latter family 

 are the various species of the Eyebright (Euphrasia), the Yellow-rattle (Rhinan- 

 thus), Cow-wheat (Melamjyyrum) and Lousewort (Pedicularis), and also Bartsia, 

 Tozzia, Trixago, and Odontites. The most extensive genera are Eihphrasia and 

 Pedicularis, the species of which, with few exceptions, are found in the northern 

 hemisphere, adorning grassy meadows with their pretty flowers, especially in the 

 arctic zone, and the high mountain regions of the Himalaya, the Altai and Caucasus, 

 the Alps and the Pyrenees. 



Little suggestion of parasitic habit is given in the first stages of development 

 of any of these plants. A seedling of the Cow-wheat within a week puts forth a 

 primary root 4 cm. long, from which half a dozen lateral roots ramify at right 

 angles without there being any attachment to a host to be noted (see fig. 34 13 - 14 - 15 ). 

 Suckers are never developed until the secondary roots have attained a length of 

 from 12 to 24 mm., and then only if the latter come into contact with other living 

 plants to their taste, a circumstance which doubtless is almost certain to happen, 



