[Vor. 1 
304 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
By means of this method one could readily observe any changes 
that might take place in the cells and make accurate compari- 
sons with controls. Frequent observations were made, and 
throughout this experiment, which continued for several days, 
one could not distinguish between the appearance of those 
sections in a drop of sterile water and those in the sterile extract 
from decayed plums. 16 is possible and perhaps probable that 
this fluid, being merely the juice of the fruit, was too dilute to 
be effective, but the experiment was made because of the 
possibility of positive evidence. 
Discussion of Results.—The initial stage in the injury caused 
by this fungus is shown by discoloration only and not by plas- 
molysis, and therefore one cannot draw conclusions with ab- 
solute certainty as to the poisoning effect of the extract on 
the cells of a cut surface, for the latter turn brown as soon as 
exposed to the air, just as when infected with the organism. 
It was comparatively easy, however, to observe that the extract 
had no effect on the cell walls, for no difference could be observed 
between the cell walls of the tissue thus treated and those of 
the control specimens. Even where the sections were left in 
the extract for several days neither swelling nor disorganization 
of the cell walls or middle lamelle was noted. When sections 
of plum tissue were inoculated with one or more spores of the 
brown-rot fungus no cell-wall disintegration resulting from the 
growth of the fungus could be observed. A comparative study 
of sections of tissue, respectively exposed and not exposed to 
the action of the extract from decayed fruit, showed that no dif- 
ference could be detected between the two, and that, therefore, 
no enzyme with a perceptible cytolytic action exists under these 
conditions. It has been held by some, notably by Behrens (6), 
that the injury to the host cell is largely physical in that the 
fungus penetrates at such a prodigious rate that the fluids of the 
host cell are allowed to escape with loss of turgor to the latter; 
furthermore, that the osmotic equilibrium is soon destroyed, 
with plasmolysis and death ensuing. It is very probable that 
part of the rapid injury to the host can be explained on purely 
physical grounds, but this may not be the only factor involved, 
although we do not now know what chemical activity of the 
fungous cells may be concerned in the rapid killing of the host 
tissue. | 
очи И 
