178 CLIMBING PARASITES. GREEN-LEAVED PARASITES. TOOTH WORT. 



base. Whereas in Thesium they never issue otherwise than laterally from the 

 ramifications of the roots, in Rhinanthaceae they are often terminal. A differentia- 

 tion into core and rind-like envelope is never clearly marked; a vascular bundle 

 runs through the middle of the sucker and is surrounded by thick-walled cells. 

 The absorbent cells are, moreover, shorter than in the Santalaceae. The individual 

 genera of the Rhinanthacese exhibit amongst themselves only very slight differences 

 in respect of their suckers. On the roots of Eyebright (Euphrasia), the haustoria 

 are tiny roundish nodules which rest upon the host's root without encompassing it. 

 The absorption-cells are very short, and only just penetrate into the host. The 

 vascular bundle is either entirely wanting within the sucker, or its place is taken 

 by a single, comparatively large vessel. On the roots of the Yellow-rattle 

 (Rhinanthus) the suckers are spherical and of considerable size (up to 3 mm. in 

 diameter); their margins are swollen and often encompass more than half the 

 circumference of the roots attacked. The absorbent cells are short but very 

 numerous. In the Cow- wheat (Melampyrum) the suckers resemble those of the 

 Yellow-rattle in size and shape and in the shortness of the absorption-cells; but in 

 the former the margins of the suckers not only embrace the roots of the host, but 

 cling to them in such a way as to penetrate their substance and form circular 

 grooves upon them. 



All the Rhinanthaceae mentioned are herbaceous annuals. Their suckers are 

 few in number, and therefore easily escape observation. By the time these plants 

 ripen their seeds any piece of a root that has been attacked has for the most part 

 already turned brown and been killed, and is in a state of decay. But shortly 

 afterwards the parasite itself withers. The comparatively large seeds, well- 

 furnished with reserve-material for the nourishment of the embryo, fall out of the 

 dry capsules, and generally reach the ground at no great distance from the mother- 

 plant and germinate there. In the autumn, close to Cow-wheat plants, which are 

 still green but have already let fall the seeds from their lowest capsules, individual 

 examples of those seeds may be seen already sprouting in the damp moss and mould 

 on the ground of woods. If they fall to earth not very far from the parent-plant, 

 the seedlings may happen to attack the host which has already had one of the 

 branches of its root sucked and killed by the latter in the previous summer. 



Nearly all these annual green-leaved parasites make their appearance in num- 

 bers close together. If, for instance, a species of Cow-wheat has taken up its 

 quarters in a particular part of a wood, there are always collections of hundreds 

 and thousands of specimens to be found together. The small-flowered Yellow- 

 rattle often grows so abundantly in damp meadows that one might suppose it to 

 have been sown by the bushel. The large-flowered, hairy Yellow-rattle is 

 similarly exuberant in ploughed fields, and the Eyebright, with its large number of 

 species, is produced in such abundance in mountainous districts that, at the season 

 when its little milk-white flowers are open, regular milky ways seem to stretch 

 across the green meadows. Millions of them are situated together rooted in the 

 grass-covered ground, and one would suppose that in course of time the growth of 



