of some Phanerogamic Parasites. 299 
These phloem-layers are separated from the cortex by one or 
two layers of parenchyma-cells, and by the pericycle. We 
have therefore in the central cylinder of the haustorium several 
bicollateral fibro-vascular bundles which later become con- 
fluent, consisting of a central xylem, two cambiums, and two 
phloems. The cambiums add not more than one row of cells 
to each side of the xylem, and two rows of cells to each 
phloem area. They then cease to divide further, and retain 
their typical form and structure. 
If now a cross-section of Cuscuta - stem be made through 
a haustorium of about the same age, we obtain a radial 
section of the haustorium which will enable us to complete 
our knowledge of its structure. We find, in the centre, the 
thick-walled lignified cells of the xylem. These are separated 
from one another by cross-walls, which are slightly, if at all, 
oblique. These cross-walls remain intact. Hence, the xylem 
is composed of tracheids only. The cross as well as the lateral 
walls of the tracheids are deeply pitted or reticulated. I have 
observed no spiral or annular markings. Bounding the xylem 
on either side are the two cambium or, if the structure be older, 
cambiform layers rich in protoplasm. Beyond these are the 
two phloems consisting of sieve-tubes and their companion- 
cells. If the section be one of a haustorium of sufficient age, 
staining with an aqueous solution of aniline blue will demon- 
strate the callus-plates in the sieve-tubes, as will be described 
further on. The rest of the central cylinder is composed 
of elongated parenchyma-cells abutting, with the pericycle 
between, on the cortex. The differentiation in the haustorium 
begins near the base and extends towards its apex. 
The same cross-section of the parasite will show that the 
haustorium, growing through the cortical parenchyma, is about 
opposite an interfascicular mass of parenchyma. The cells of 
this interfascicular parenchymatous mass, which are adjacent 
to two fibro-vascular bundles, begin to differentiate in two 
ways along two lines on each side. Running toward the base 
of the haustorium, from the xylems of the two bundles, one 
finds two rows of cells of considerable diameter (see Fig. 12 t\ 
