CLIMBING PARASITES. GREEN-LEAVED PARASITES. TOOTHWOKT. 179 



<frass afc sucli places would be iiijuretl. This conclusion appears to be supported 

 by the assertion of the country folk that after the season when the Eyebright is in 

 full bloom, the cows yield less milk, a fact which explains the German name of 

 " Milchdieb " (milk-thief) popularly given to the plant. The diminution in the 

 quantitj^ of milk yielded is, however, certainly connected with other circumstances. 

 It depends especially upon the universal abatement of the growth of grasses in 

 carljr autumn and the consequent curtailment of the food afforded by the pastures. 

 The mjury done by the Eyebright to its hosts by the withdrawal of nutriment 

 and destruction of rootlets cannot be very considerable, for the appearance of the 

 grasses and other host-plants, which are affected, is not noticeably different from 

 that of the plants of the same kind which escape invasion. 



The same statement is true in the case of the various species of Lousewort 

 (Pedicidaris), almost all of which are meadow-plants; that is to say, they are 

 present in great abundance in upland and alpine pastures without apparently 

 injuring the species growing in their company and used by them as hosts. Unlike 

 the species of Cow-wheat, Yellow-i-attle, and Eyebright, however, nearly all the 

 Louseworts are perennial, and accordingly differ from them also in the construction 

 of their suckers. There is, it is true, no difference in shape between the suckers of 

 the Cow-wheat and those of Pedicularis, but they are dissimilar in respect of size 

 and place of origin. The suckers of the perennial Louseworts are barely more 

 than half the size, and are only developed near the attenuated exti-emity of a 

 rootlet. They are very few in number; each of the long, thick, fleshy rootlets, 

 proceeding from the base of the stem usually produces a single sucker only which 

 settles upon the root of a suitable host-plant in the same way as the suckers of 

 Cow-wheat. By the time that the parasite's fruit ripens, the piece of root which 

 has been invaded has usually already turned brown and fallen into decay. Now in 

 the case of Cow-wheat it may undoubtedly be immaterial whether the piece of root 

 attacked by it is living or not when its fruit is ripening, inasmuch as its own 

 annual root rots as soon as the seeds have been produced from the flowers above 

 ground. But witli Pedicularis it is different. The perennial roots of this plant 

 require a host to nourish them next year, and when the piece of a host's root which 

 has been attacked and sucked as a nutrient substratum one year dies, the sucker 

 belonging to the root parasitic upon it is no longer in a position to fulfil its function 

 by continuing to absorb fresh juices. Suckers thus reduced to a state of quiescence 

 soon perish, and only leave little scai's to indicate the places where they existed. 

 The perennial root of the Pedicidaris has now to seek a new source of nutriment, 

 and this is effected by the elongation of its tip, which continues to grow until it 

 reaches the living i-oot of another plant suitable as host, whereupon it develops a 

 fresh sucker upon that root. This elongation doubtless requires a large quantity of 

 plastic materials; but these are found stored in abundance in the older parts of the 

 parasitic root. 



These circumstances explain, at anyrate in part, the characteristic structure and 

 disproportionate length of the roots of Pedicularis. From all i-ound the short erect 



