Aug. i, 1921 
Studies in the Physiology of Parasitism 
611 
more substances. Similar results were obtained by Ward ( 16) and Kiss- 
ling (11). 
The work of Ward calls for special consideration. He grew Botrytis 
in culture and used the liquid on which the fungus grew, as well as a 
watery extract of the mycelium, to macerate living material and came to 
the conclusion that the entrance of the hyphae into the tissue depends 
upon the excretion of a ferment which dissolves the cellulose. Maceration 
was in most cases slow, which was probably due to the fact that cultures 
3 weeks or more old were used. Further observations of Ward led him 
to conclude that the ferment sometimes accumulates to such an extent 
at the tips of the hyphae that the cellulose of the latter is dissolved and 
the ferment and protoplasmic contents of the cells pass out in the form 
of small droplets. 
Nordhausen ( 12 ) used chiefly the extract from old mycelium, and came 
to the conclusion that the action on plant tissue was both enzymic and 
toxic in nature. He did not exclude the possibility that oxalic acid which 
was secreted by Botrytis might play a part. Behrens (2), on the other 
hand, used the expressed juice from fruits that had been decayed by 
certain fungi. In one case he employed the expressed juice of a pear 
infected with Mucor stolonifer Ehrb. and in another that of an apple 
infected with Pcnicillium luicum Zukal. He found these juices to be 
toxic to plant tissues even after boiling, and from these results he con¬ 
cluded that the toxic substance was neither volatile nor enzymic. In one 
case the fungus was allowed to grow three months before the extract was 
obtained. 
Smith (14) compared the mycelial extract of Botrytis with weak solu¬ 
tions of oxalic acid on stems of lettuce. He found that the oxalic acid 
alone induced a macerating effect on the tissue similar to that of the 
extract of the fungus material, and on the basis of these results came to 
the conclusion that the dissolution of the cell walls noted is due to the 
oxalic acid secreted by the fungus. 
So far as bacteria are concerned Potter ( 13) and Van Hall (8) found that 
Pseudomonas destructans Potter and Bacillus omnivorus V. Hall, respec¬ 
tively, produced enzyms which were able to dissolve the constituents of 
the cell walls of plant tissues so that coherence was lost. Potter worked 
both with the expressed juice of a turnip rotted with the organism and with 
the solution on which the bacterium had grown. He claims that a toxic 
substance was produced, since the boiled expressed juice from a rotted 
turnip caused the death of the cells of a raw turnip. He found that the 
organism when grown in Pasteur’s solution produced oxalic acid which 
acts as a powerful toxic agent. It is claimed that the oxalic acid then 
acts as a toxin in killing the cells and that it may also play some part in 
the dissolution of the middle lamella. In this direction the most impor¬ 
tant work with bacteria is that of Jones (jo), who carried on extensive 
researches with Bacillus carotovorus Jones. He found that this organism 
