1 14 Peirce . — A Contribution to the 
passes (at generally a right angle) through the wall of the 
parenchyma-cell, with the wall of that cell, so that not only 
does no opening by the side of the papilla exist, but it is 
impossible to determine exactly where the wall of the paren- 
chyma-cell ends. The fusion is so perfect that the transition 
from older to newer cellulose, from parenchyma-wall to 
papilla-wall, is most gradual ; they have modified each other 
in their perfect union. It seems to me by no means improb- 
able, though micro -chemical and optical proofs are still 
wanting, that the rapid growth of the haustorial papillae is in 
part at least made possible by the walls which cover their tips 
not being quite solid ; that indeed the enzyme which dissolves 
the walls of opposing cells also keeps the walls at the tips of 
the cells which secrete it in partial solution, and therefore in 
such condition that they but slightly resist the forward pres- 
sure from within. Careful staining by chlor-iodide of zinc, or 
by various agents producing more enduring stains (e. g. Congo 
Red), fails to show the slightest evidence that the wall of the 
cortical parenchyma-cell persists as a sheath around the 
papilla, and that the protoplasmic and other substances in its 
cavity are separated and protected from the haustorial cell by 
an involution of its wall. Its wall has become a constituent 
and indistinguishable part of the wall of the intruding cell, 
acting no longer as a protection against, but as a part of, the 
intruder. 
We thus see that the haustorial cells penetrate those 
opposed to them. That this penetration is accomplished 
by means of chemical action as well as by pressure we see 
from the walls with which they come into contact becoming 
thinner at the points of contact as they bend in, and finally 
disappearing at these points, and from the fact that the 
holes through which the intruding cells pass are accurately 
proportioned to them in form and size. Through the repeated 
perforation of their walls by successive haustorial cells, the 
cortical cells which oppose the progress of the haustorium are 
removed, and along this tunnelled way the young haustorium 
reaches, and finally applies itself to, the conducting tissues of 
