77 
Physiology of the Genus Cuscuta. 
the parasite was by some means closely fastened to the pith. 
Cross-sections through the haustoria and the pith showed 
several interesting features. The epidermal cells were quite 
as long, papillate, and thin-walled as if they had developed in 
contact with a host-plant ; their protoplasmic contents were 
only slightly less abundant and granular than in normal con- 
ditions ; and they had penetrated the second, in some cases 
the third, layer of parenchyma-cells. (Of the mode of pene- 
tration I shall have occasion to speak in Part II of this paper.) 
The haustoria underlying these well-developed epidermal 
cells had advanced very considerably in their development, 
and were evidently pushing themselves against and through 
the adjacent cortical cells, though more slowly than normal. 
Their structure was as complete as that of young haustoria 
about to penetrate a host but still imbedded in their cortical 
matrix. That they were not farther developed, had not 
penetrated the overlying cortex and entered the stick of 
pith is not surprising ; for the pith, though impregnated to 
a distance of a millimetre or more from the surface with 
a decoction of a plant, was nevertheless a comparatively 
innutritions substance. The decoction at first contained 
somewhat more nutritive matter than would at once be avail- 
able in a host, but it was not constantly renewed as is the 
case in the living host, and it was likely to be very largely 
consumed by the epidermal cells, and also by the Bacteria 
and Fungi which are so difficult to exclude when it is not 
possible completely to sterilize everything used in an experi- 
ment. Yet the almost complete development of the epidermal 
cells, and the very considerable development of the haustoria 
plainly show, when taken in connexion with the results of 
the other experiments just described, that neither contact 
alone, nor nourishment alone after a period of contact, is 
sufficient for the complete development of these two asso- 
ciated structures. Both continued contact and abundant 
nutrition from without are necessary for full development. 
I have previously pointed out that food taken into the 
parasite in one region can be transferred to another region at 
