Development of Cassytha filsjormts, L. 409 
lar. The cells also contain chloroplasts and considerable 
protoplasm with large round nuclei and nucleoli. Internal 
to this is a zone of hard bast (3), broken by rays of large 
cortical cells into smaller and larger patches, rather irregu- 
lar in arrangement. The bast cells are somewhat larger 
than the phloem cells, but smaller than cortical cells and the 
lumen is reduced to a minimum. Beneath each patch of 
hard bast is an irregular space, formed by the degeneration 
of phloem, of which the flattened remains usually appear on 
the inner border of the space (Fig. 4), but which seem on 
the whole very feeble and unimportant. The rays separat- 
ing these patches contrast somewhat with the outer cortical 
cells, with which they are continuous, in their larger size 
and comparative. emptiness. 
The wood is arranged in a continuous ring beneath the 
phloem patches. In the old stem medullary rays are faintly 
recognizable. The wood elements grow larger toward the 
centre of the stem, and the most internal elements are very 
large pitted vessels, eight to ten in number (5). 
Extending far into the pith are five to seven patches of 
delicate internal phloem cells (8), each patch enclosing three 
or four thickened cells of protoxylem (7), in rows or 
separate. The pith consists of large cells with intercellular 
spaces and without starch or protoplasmic contents. They 
have very thin walls and look quite empty. 
A study of the parts of the mature stem in detail shows 
the epidermis to be provided with copious stomata, placed 
transversely on the stem, and arranged in longitudinal rows, 
which are slightly depressed below the surface, as has been 
already noted by Hackenberg * and other authors. As 
the stomata lie transversely, the cross section presents the 
appearance given by longitudinal sections of ordinary plants, 
and the usual appearance of two adjoining guard cells must 
be sought in the longitudinal section. The stomata are in 
* Verhandl d. naturhist. Vereims d. Rhein. u. Westfalen, V. 6, 
Bonn, 1889. 
