CLIMBING PARASITES. GREEN-LEAVED PARASITES. TOOTHWORT. 177 
seeing that the lateral roots are numerous and are sent out in all directions from the 
main root, and therefore must inevitably come across the root-systems of other plants. 
The seedling in perennial species of Thesiwm develops comparatively slowly. 
It reaches a length of from 3 to 4 em. in the first year, sends a tap-root into the 
earth, and puts forth a few branchlets, which do not fasten upon the roots of other 
plants by means of suckers until several weeks after germination. ‘These suckers 
are relatively large in all species of Thesium, and they catch one’s eye the moment 
the roots of a plant are carefully divested of earth. They are then recognized, 
as may be seen in fig. 361, as little white knobs, which stand out clearly from the 
dark earth and are always inserted laterally upon the secondary roots. They are 
Fig. 36.—Bastard Toad-flax (Thesium alpinum). 
1 Root with suckers; natural size. 2 Piece of a root with sucker in section; x35, 
constricted near their insertion, and the strangulated portion often gives tbe 
impression of being a pedicel upon which the knob is seated. This knob is 
differentiated into a central core and a multicellular, cortical coat enveloping it. 
The cellular coat rests upon the root of the host attacked, and does not merely 
adhere to one limited spot, but spreads itself out over the root like a plastic 
mass, and forms a cushion surrounding about a fourth or fifth part of the cireum- 
ference (see fig. 36?) without, however, penetrating into the substance of the root. 
There are in the core two strands or bundles of vessels, and between them small 
cells arranged in rows, from which absorption-cells arise at the spot where the 
sucker first applied itself to the nutrient root. These absorption-cells grow out 
beyond the rind-like envelope round the core, perforate the cortex of the host, 
penetrate into the wood at the centre of the invaded root, and there diverge like 
the hairs of a dry paint-brush. 
The suckers of the green-leaved Rhinanthacee are on the whole similarly 
constructed; only they are relatively smaller and more delicate, being sometimes 
almost translucent, and they are either not at all or only slightly constricted at the 
Vou. I. 12 
