I I 2 
Peirce.— A Contribution to the 
case we should expect to find not merely small parts of the 
wall, and these of shape and size proportioned to the attacking 
cells, but large portions gone, in fact a general disorganization 
of the tissue in the region attacked. No such changes in the 
attacked tissues of a host occur, and hence we cannot suppose 
that the host destroys its own tissues to any extent. That 
the haustorial cells are chemically active is strongly indicated 
in two ways. First, a study merely of alcohol-material inclines 
the observer to doubt that such accurate adjustment of the 
phloem- and xylem-elements in the central cylinder of the 
growing haustorium with the phloem- and xylem-elements of 
a vascular bundle of the host could be accomplished by 
mechanical means alone. How accurate this adjustment is, 
even to the correspondence of thick and thin areas in the 
walls of the haustorial tracheids with similar areas in the 
walls of the tracheae of the host to which they apply them- 
selves, I have already demonstrated \ Second, thin sections 
of young haustoria of C. glomerata in the fleshy stems or 
petioles of Impatiens Balsamina show that the long papillate 
cells at the tips of the haustoria pass through the walls of the 
opposing parenchyma-cells of the host in the same way as do 
the papillate cells of the pre-haustorium. 
In the experiment with elder-pith it is evident that the 
dead pith-cells cannot form new walls, but in a living plant 
one must determine accurately whether, when a papillate 
haustorial cell applies itself to a living parenchyma-cell of the 
host, the wall of the parenchyma-cell be simply pressed in by 
the force of the growing haustorial cell ; whether the natural 
extensibility of the cell-wall thus being gradually pushed into 
the cavity of the cell, be supplemented by growth leading to 
the development of the at first shallow depression into a cup, 
and finally a cylindrical pocket, enclosing the haustorial cell ; 
or whether there is actual perforation of the wall of the paren- 
chyma-cell, and whether the thin wall of the papilla is in 
actual contact with the protoplasmic and other contents of 
the cell into which it has grown. A careful study of thin and 
1 Loc. cit. p. 300. 
