certain Species of the Genus Christisonia. 1 1 1 
seen in a section not quite median, which does not pass 
through the vascular strand ; the latter becomes differentiated 
as the haustorium grows out from the cortex, and eventually, 
when it reaches the central cylinder of the host, a continuous 
chain of xylem-elements is laid down, extending from the 
central cylinder of the root of the parasite, through its tissues 
and those of the haustorium, to where a direct union is 
effected between the vascular tissue of the haustorium and 
that of the central cylinder of the host-root. The main 
portion of the haustorium is built up of slightly elongated 
cells, with dense contents and conspicuous, large nuclei. 
Their function may consist in the conduction and storage 
of proteid matter. No sieve-tubes were anywhere discovered. 
The haustorium sometimes occupies almost the entire dia- 
meter of the host-root and destroys a large area of its tissues. 
The haustoria attached to one piece of root were all com- 
pletely filled with dark fungus-spores and hyphae, which also 
occupied part of the tissues of the host-root, as well as a few 
of the cortical cells of the root of the parasite ; they were 
sufficiently numerous to interfere with the work of the 
haustorium in absorbing food from the host. 
From the above description of the development of the 
haustorium, it will be seen that it is of exogenous origin 
(Fig. 22 ) ; there is no evidence to show that it arises from 
any of the internal layers of the cortex ; it appears simply 
to be formed by a direct outgrowth from the surface of the 
root, as is the case in the roots of Rhinanthus , and not in the 
mode described for Cziscuta 1 and others. 
Anatomy of the Stem. 
A transverse section of the stem shows an almost complete 
ring of vascular tissue ; the band is broken at the place of 
insertion of the leaf-trace bundles, two or three of which 
1 On the Structure of the Haustoria of Phanerogamic Parasites, by G. J. Peirce ; 
Annals of Botany, Vol. vii. No. 27. A Contribution to the Physiology of the 
Genus Cuscuta, by G. J. Peirce, Annals of Botany, Vol. viii. No. 29. 
