109 
Physiology of the Genus Guscuta. 
side by the intruders, undoubtedly also dissolved the cellulose. 
By this solvent action exerted on the walls of the cortical 
cells of the host, the food-substances contained therein can be 
reached and be appropriated later by the papillate cells. The 
holes thus dissolved, constantly increasing in number and, as 
I shall presently show, in size by the solvent action of the 
cells at the tip of the haustorium proper, enable the young 
haustorium to grow rapidly forward through but feebly 
opposing tissues toward the conducting- tissues of its host. 
That the cellulose thus dissolved is probably consumed by 
the parasite is indicated by the normal development of the 
papillate epidermal cells, and the very considerable develop- 
ment of the haustoria formed by those branches twined about 
sticks of pith saturated with decoctions. For, though the 
decoction is nutritious at first, it so rapidly deteriorates in 
nutritive value that it can be useful for only a short time, 
and the pith, containing of itself no food of any kind except 
the cellulose of its walls, must be extremely innutritious. 
The epidermis which covers a haustorial swelling consists 
of two sorts of modified cells : those lying directly over the 
haustorium become separate from one another, except at their 
bases, and grow out into long papillae : those surrounding 
them, and therefore not in, though parallel with, the line which 
the growing haustorium will follow in penetrating the host, 
elongate but do not separate from one another, and hence do 
not become papillate. The walls at their tips are very nearly 
as thin as those of the papillae. Both sorts of cells come into 
intimate contact with the walls of the epidermal cells of the 
host. The papillate cells exercise a solvent action so ener- 
getic that holes are made through the walls of those cells that 
oppose their further growth. The non-papillate cells, like the 
others in the kind, but not in the amount, of new growth which 
they accomplish, also excrete a solvent through their terminal 
walls, but the quantity of solvent excreted is not large. By 
this means only a partial solution of the walls of the epidermal 
cells of the host with which they are in contact takes place, 
but the walls of the contiguous cells of parasite and host 
