1 IO 
Peirce —A Contribution to the 
become fused together so perfectly that (Fig. 4) they are 
quite indistinguishable from one another. This union is very 
firm, as is shown by the resistance encountered in tearing the 
parasite away from its host even before the haustoria have 
penetrated. This union is sometimes broken after a time by 
the pushing apart of parasite and host owing to the forcible 
penetration of the haustorium through not readily soluble 
tissues, but in such cases the walls of the cells, once firmly 
united and then torn apart, are irregular and ragged. 
I have already pointed out (p. 61) that the parasite can 
twine about leaves and send haustoria into them. The curve 
of the parasite about the lamina of a leaf can be only an 
ellipse. Manifestly in such a case as this there can be but 
little of the mechanical advantage which aids the haustoria in 
penetrating an approximately cylindrical stem. The stem of 
the parasite no longer furnishes an unyielding brace on which 
the haustoria are based ; consequently it will be pushed away 
from the surface of the leaf by the growth of the haustorial 
swellings, just as the leaf too bends away under the same 
pressure. Evidently by pressure alone the haustoria would 
only with great difficulty penetrate the leaf. The rejuvenated 
epidermal cells of the parasite, however, perform the same 
work as before. The tips of the non-papillate £ cushion-cells ’ 
fuse with the walls (which they partially dissolve) of the 
opposite epidermal cells of the leaf, and the leaf is thus 
securely held. The papillate cells, collectively the £ pre- 
haustorium,’ perforate the walls of the cells opposite them by 
a more complete solution than that accomplished by the 
f cushion-cells,’ and, growing through the holes thus made, 
enter the mesophyll. Held fast against the leaf by the 
e cushion-cells,’ and anchored by the pre-haustorial papillae, 
the stem of the parasite can now brace, and so assist, the 
haustoria in their forward growth. Although one ‘ cushion- 
cell ’ holds parasite and host but feebly together, yet there 
are so many of them that the attachment becomes very firm. 
The area of attachment is large ; through the centre of this 
area the haustorium grows ; its tip is conical, not blunt, and 
