14 -TWO SORTS OF PARASITES. 



But it is manifest that those which are leafless 

 cannot do so ; they require sap previously con- 

 verted into proper juice, or descending sap in 

 the plants to which they belong, having no 

 organs of their own capable of effecting this 

 essential process of vitality. Accordingly, 

 they are found growing from the roots of their 

 peculiar vegetables, which they rob of the 

 cambium, or sap, that comes down after being 

 elaborated in the leaves. We have a notable 

 instance of such a. parasite in the common 

 cuscuta, or dodder, which attacks clover, and 

 that sometimes to an alarming degree. Of 

 late years complaints have been made that it 

 has been found in great quantities on the 

 plants of clover raised from foreign seed ; and 

 it would be well to pay attention to the tho- 

 rough cleansing of it, after importation, from 

 so dangerous an accompaniment. Another 

 common parasite of this species, found also on 

 clover, is the orobanche, or strangle-vetch. It 

 is so called from the Greek words opo(3og, 

 {07'obos,) a vetch, and ayx^iv, {angkein,) 

 to strangle. It fastens first on the roots, but, 

 unlike the dodder, afterwards sends out its 

 fibres into the soil. 



The parasites to which reference will first 



