of some Phanerogamic Parasites. 293 
mother-stem, develop no farther, remain abortive, and are 
made evident only by swellings of greater or less size. The 
epidermal and cortical tissues have been pushed out by the 
subjacent growing haustoria, and though the epidermal cells 
may have begun to differentiate in the way to be described 
further on, they do not greatly differ from their neighbours, 
and furnish an unbroken and normally cutinized protective 
covering. In these abortive haustoria no differentiation of 
tissues takes place, the cells remaining parenchymatous. Such 
a haustorium, early aborted, is shown in transverse section by 
Fig. 2', PI. XIII. 
Cuscuta americana , as shown by Fig. 1, twines from left to 
right around its host in a spiral sometimes short and close, 
oftener long and loose. The outline of the haustorium as 
seen in superficial view (see Fig. 1, c, d, PI. XIII) is elliptical. 
The long axis of this ellipse is not parallel with the axis of 
the parasite, but is approximately parallel with the long axis 
of the host. According as the spiral formed by the parasite 
in twining about its host is steep or gradual, the long axis 
of the ellipse is at a lower or higher angle with the long axis 
of the parasite. In this way the conducting elements of the 
haustorium are so oriented as to be in the best possible 
position for uniting with the corresponding elements in the 
host. 
The form and structure of a young stem two or three 
centimeters above the youngest haustorium is shown by the 
cross-section in Fig. 2. The outline is approximately round, 
with more or less pronounced lobes. The epidermis, seldom 
if ever interrupted by stomata and bearing no trichomes, 
consists of a single layer of rather small cells, well supplied 
with protoplasm, whose outer walls are thickened and cutin- 
ized. Between the epidermis and the pericycle is a parenchy- 
matous tissue whose cells are of two sorts. About midway 
between the pericycle and the periphery is a more or less 
wavy and somewhat broken line composed of small, irregular, 
rather compressed cells. Their irregularity is due to the 
torsion of the stem. The rest of the cortex consists of large, 
