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 Thesiuvi develops comparatively slowly. 

 It reaches a length of from 3 to 4 cm. 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 recog-nized, 

 as may be seen in fig. 36 ^, 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. — Bast.ird Toad-flax {Thesium alpinuni). 

 1 Root with suckers; natural size. 2 Piece of a root witli suclcer in section; x35. 



constricted near their insertion, and the strangulated portion often gives the 

 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 circum- 

 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 Rhinanthacese 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 



Vol. I. 12 



