820 



A TEXTBOOK OF THEORETICAL BOTANY 



the long cells of the point take on independent growth and spread through 

 the tissues. A strand of xylem and phloem now differentiates in the sucker 

 and makes connection between the vascular tissues of the host and the cor- 

 responding tissues in the Cusciita. 



i— Host root 



Haustorium 



Lathraea root 



*<# 



,<- 









Haustorial sucker 



r--'*^ii^^^-- 'f Haustorium 



',3, <■ f •i.jr 



^^ c r 



Cortex of grass 

 root 



B 



Fig. 817. — Haustorial roots of parasites. A, Lathraea 

 squawaria (Toothwort) on Elm. B, Pedicidoris 

 syhatica (Lousewort) on a grass root. 



In all the above cases of parasitic attachments the vascular tissues of the 

 host are the object of the attack, and substances are deflected from them into 

 the parasite. It is difficult to find a common morphological basis for all 

 such parasitic attachments, but they are sufficiently uniform in function to 

 be grouped together biologically, and they are given the name of haustoria. 

 The peculiar attachment organs of the ]\Iistletoe will be reserved for 

 treatment later (see Volume IV). 



