294 Peirce . — On the S true hire of the Haustoria 
thin-walled cells with fairly abundant protoplasm. Small 
intercellular spaces are numerous. Just within the pericycle 
one finds a somewhat irregular ring of lactiferous tubes, large, 
thick-walled, and angular in cross-section. The small fibro- 
vascular bundles are separated from one another by masses 
of parenchyma-cells like those which compose the pith, large 
and thin-walled. The fibro-vascular bundles are of the col- 
lateral open type, but with more phloem than xylem. The 
phloem consists of soft bast only, no hard bast or scleren- 
chyma-fibres ever being developed in the stem. The xylem 
consists of ducts and wood-cells. The ducts earliest formed 
are soon resorbed, leaving a large air-space. The cambium 
may always be clearly seen. 
In a radial section (see Fig. 3) through a bundle, one sees 
that the bundles are sharply marked off from the funda- 
mental tissue in the centre of the stem by the large air- 
space ( a ) ; that the ducts (d), either reticulated or more 
commonly pitted, are few in number ; that the cambium- 
cells (c) are not so long as the elements developed from them ; 
that the long sieve-cells form tubes of very considerable 
diameter (s), and on their horizontal walls thick callus-plates 
are formed ; that the companion cells (c. c ) are sometimes 
longer than the elements of the sieve-tubes, and have more or 
less oblique terminal walls ; that all the elements of the 
bundle are thin-walled. 
Making now a radial section in the region just above the 
youngest haustorium, the new haustorium is found to originate 
in the cortical parenchyma just beyond the pericycle, in 
a longitudinal line of cells which, by rapid successive divisions 
in a tangential direction, soon form a mass of the shape of 
a plano-convex lens, whose convexity is toward the periphery 
of the stem. By the growth and division of these cells the 
structure assumes a conical shape (see Fig. 4), the cells at 
the base being long, those toward the apex becoming smaller, 
until the minimum is reached in one or two rows from the 
tip. The tip consists of long, rather narrow cells. The two 
or three rows immediately behind the tip are made up of 
