of some Phanerogamic Parasites . 315 
have studied in this paper. Its morphology and physiology 
are the same; it is a lateral root modified in structure to 
conform with the special conditions to which it is exposed and 
the special work which it has to do. It differs from the other 
haustoria only in its smaller size, and the consequent smaller size 
of its elements ; it is structurally and physiologically as perfect. 
CUSCUTA EUROPAEA, L. 
The haustoria of this plant differ in no essential respect 
from those of the preceding species. They are larger than 
those of C. epilinum and C. epithymum. In them I have 
found the same bi-collateral structure of the central cylinder, 
a strand of tracheids bounded by cambiform cells which in 
turn are bounded by sieve-tubes and companion-cells. The 
conducting elements of both xylem and phloems unite directly 
with the corresponding elements in the host, and furnish an 
unbroken connection between the conducting tissues of the 
parasite and its host. 
One might have concluded from a priori considerations 
that such successful parasites as the Cuscutas must have their 
haustorial structures well adapted for the conduction of 
nutrient solutions of various sorts which they must draw from 
their hosts, and that these conducting tissues would be applied 
to the corresponding tissues of the host-plants in such ways 
as to do their work most perfectly. After the comparatively 
small amount of food stored in their seeds is consumed, the 
Cuscutas are absolutely dependent upon their hosts for food. 
Since they contain extremely little chlorophyll they must draw 
non-nitrogenous foods, sugar, and so forth. For the further 
elaboration of these they must have certain mineral salts and 
inorganic nitrogen-compounds. We should therefore expect to 
find, what has long been known to be the case, that the haustoria 
contain xylem-elements for the conduction of these last two 
sorts of substances. It is through the sieve-tubes that carbo- 
hydrates are conducted. We should therefore expect to find 
