328 Brown.—Shidies in the Physiology of Parasitism . /. 
E. Action of Extract on Tissues. 
(a) General Account. 
The action of the extract is of a twofold nature : 
1. Solution of certain constituents of the cell-wall, resulting in loss of 
coherence of the tissue. 
2. Death of the cells themselves. 
These two aspects of the phenomenon will in the meantime be referred 
to respectively as the ‘ macerating ’ and ‘ lethal ’ actions of the extract. 
Fleshy tissues were prepared in the way described in the preceding 
section. The following tissues were tested and found to be readily acted 
on: Tubers of Potato , roots of Turnip , Beet , Radish ; fruit tissue of Apple , 
Cucumber ; pith of stem of Senecio articulata . With extract of normal 
strength, potato discs of \ mm. thickness are very usually disintegrated in 
twenty to thirty minutes, though, as has been stated, there may be con¬ 
siderable individual variation. Discs of white or yellow Turnip require as 
a rule a similar time, while the harder tissue of Swedes is more slowly acted 
upon. The above list is no doubt capable of wide extension, and it is 
indeed highly probable that the fleshy parenchymatous tissue of fruits, 
tubers, &c., is very generally susceptible to the action of this fungus 
extract. 
Tissues of leaves, petals, &c., were treated in a variety of ways. Discs 
of these were submerged in the active extract, so that action proceeded 
from the margin (the cuticle presenting an impenetrable obstacle to the 
diffusion of the extract, as will be shown in a subsequent paper), or the 
extract was injected into the tissue by means of the air-pump. In a series 
of experiments the extract was injected into the tissue by means of a hypo¬ 
dermic syringe. The advantage of this method is that the tissues are main¬ 
tained in a more normal condition during the course of the action than 
when they are submerged in liquid. 
When the discs are merely submerged in the extract the action may 
be comparatively slow, being to a large extent limited by the rate with 
which the leaf disc becomes injected. This injection process, which also 
takes place when the discs are immersed in water, is somewhat obscure in 
principle; 1 in particular the fate of the air of the intercellular spaces is not 
quite clear. Injection proceeds chiefly along the line of the vascular 
bundles, especially from the proximal end. The course of the action is also 
influenced by the mechanical properties of the leaf discs. Thus, in the case 
of tulip petal discs, the disintegration of the more sensitive central tissue 
1 This phenomenon is probably related to that of the ascent of water in shoots which are kept 
in a saturated atmosphere. The injection would thus be due to an active pumping action on the 
part of the cells of the leaf; cf. Dixon, Proc. Roy. Ir. Acad., vol. iv, 1896-8, p. 627. 
