PHYSIOLOGY 



229 



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. 202 at the left). 

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

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

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



Fio.- 202. O'."-"'" MtrtgKUO. On the viiiht. ^erniinatiiu; * ilin^s. In the middle, a plant of 



Csotai parasitic on a Willow twij; : V reduced leaves : III. flower-clusters. On the left, cross- 

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

 ]>arenehyim anil in intimate contact with the xyleni r and the phloem < of the vascular 

 bundles; .*, displaced cap of sheathing sclerenchyina. 



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

 and^only its light yellow, reddish-brown or amethyst-coloured flower-shoot' appears 

 above the surface of the ground. Orobanchc, like Cuscuta, contains a small 

 amount of chlorophyll. Both are dreaded pests ; they inflict serious damage upon 

 cultivated plants, and are difficult to exterminate. 



Many exotic parasitic plants, especially the Rafflesiaceae, have become so 

 completely transformed by their parasitic mode of life that they develop no 

 apparent vegetative body at all ; but grow altogether within their host plant, 



