224 



BOTANY 



PAra" I 



of the host plant by means of solvent ferments and the pressure resulting from 

 their own growth. They invade the tissues of the host, apparently without 

 difficulty, and fasten themselves closely upon its vascular bundles, while single 

 hypha-like filaments produced from the main part of the haustoria penetrate the soft 

 parenchyma and absorb nourishment from the cells. A direct connection is formed 



Fig. 196. — Cuscuta europaea. On the right, germinating seedlings. In the jnidrlle, a plant of 

 Ctiscuta parasitic on a Willow twig ; h, reduced leaves ; Bl, flower-clusters. On the left, cross- 

 section of the host plant W, showing haustoria H of the parasite Cus, penetrating the cortical 

 parenchyma and in intimate contact with the xylem v and the phloem c of the vascular 

 bundles ; s, displaced cap of sheathing sclerenchyma. 



between the xylem and phloem portions of tlie bundles of the host plant and the 

 conducting system of the para.site, for in the thin- walled tissue of the haustoria 

 there now develop both wood and sieve-tube elements, which connect the corre- 

 sponding elements of the host with those of the parasitic stem (Fig. 196 at tlie left). 

 Like an actual lateral organ of the host plant, the parasite draws its transpiration 

 water from the xylem, and its plastic nutrient matter from the phloem of its host. 

 The seeds of Orobanche (Broom rape), another parasite, only germinate when in 

 contact with the roots of the host plant ; only its haustoria penetrate the roots. 



