114 Smith oil StnicUirc and Parasitism 



roots of the above-mentioned species of Orobanchc. They 

 do not seem to be present in Apliyllon^ but as I have not 

 obtained any verj' young stages, it is possible that the root- 

 caps are formed here also, and later slough off. 



Parasitic Connections. 



Parasitic connection with the host is effected by large 

 haustoria, which fasten upon the host-root. The Aster roots 

 are usually less than half the diameter of the Aphyllon root, but 

 are harder and more woody. As a rule, they are not shriveled 

 beyond the point of contact, but pass through the cluster of 

 Aphyllon roots and enter the soil beyond them. The host- 

 root is not completely surrounded by the sucker, but usually 

 remains distinct and quite unmodified in structure on the side 

 away from the parasite. The sucker is covered with an 

 epidermal layer similar to that over ordinary Aphyllon roots, 

 and this is quite continuous with the epidermis of the host- 

 root. Beneath the epidermis the haustoria are composed of 

 parenchymatous tissue, with strands of bundle-tissue, which 

 branch almost at right angles from the bundle-tissue of the 

 main root. This parenchyma spreads and mingles with the 

 parenchyma of the host so intimately that it is impossible to 

 distinguish their boundaries (Plate XIV, Fig. 2). The xylem 

 and phloem elements of the parasite pass into the xylem and 

 phloem regions of the host, and mingle with the correspond- 

 ing elements of the host-bundle. The general position of the 

 bundle of the host, is little modified however, and there seems 

 to be no separation and isolation of bundle elements from the 

 host-root within the tissue of the parasitic tubercle, such as 

 occurs in Conopholis} 



' L. L. W. Wilson," Observations on Conopholis Americaita, Bot. Contrib. 

 Univ. Penn., vol. ii, p. 12. 



