114 Smith on Structure and Parasitism 
roots of the above-mentioned species of Ovobanche. They 
do not seem to be present in Aphyllon, but as I have not 
obtained any very 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 Aphy//on root, but 
are harder and more woody. Asa 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.' 
1L. L. W. Wilson, Observations on Conopholis Americana, Bot. Contrib. 
Univ. Penn., vol. ii, p. 12. 
