330 Brown—Studies in the Physiology of Parasitism . /. 
rotting nor any invasion by the fungus. The slight effects observed were 
set down to bacterial contamination, the cultures having become by this 
time very foul. In another experiment, pieces of Pellia thallus, leaves of 
Mnium and Plagiochila as well as portions of various higher plants (leaves 
of Geranium , Dahlia , petals of ditto) were placed on a plate of germinating 
spores, set up as previously described, control pieces being placed on 
a similar plate from which the spores were absent. In the course of 
twenty-four hours the Geranium and Dahlia tissues were largely invaded 
and decomposed; after forty-eight hours they were entirely rotten, while 
the controls were still unchanged. On the other hand, up to the end of 
the experiment, which lasted for four days, the moss and hepatic tissues 
appeared quite unaffected, although they had been completely overrun by 
the fungus. 
The conclusion from these experiments, viz. that mosses and hepatics 
show a considerable degree of resistance to the attack of Botrytis, seems 
more in accordance with experience than the results of Nordhausen. The 
habitat of these plants is one which would be calculated to encourage 
the growth of the fungus. If they are as highly susceptible to attack 
by the fungus as Nordhausen states, it is surprising that no natural occurrence 
of the latter on these plants has been described. Apart from the experi¬ 
ments of Nordhausen, there appears to be no case of infection of mosses by 
Botrytis recorded. 1 
Among Algae, the action of Botrytis extract was tested on filaments of 
Spirogyra. From the two tests made in this connexion it appeared doubt¬ 
ful whether any action occurred. If any, it was certainly very slight. 
Here by way of contrast it may be mentioned that experiments with 
the filamentous staminal hairs of Tradescantia virginica gave a strong 
positive result, the filaments rapidly breaking up into the individual cells, 
from which the coloured contents soon became discharged. 
Viewed generally, the macerating action of the extract shows itself 
in the tissue losing completely its coherence, subsequently breaking down to 
form a mush, and in extreme cases passing almost completely into solution. 
With regard to the lethal action, the criteria must to a large extent be 
chosen to suit the particular circumstances. In the case of such tissues as 
turnip or cucumber, the lethal action of the extract can be demonstrated by 
failure of the cells after a time to show plasmolysis in hypertonic solutions. 
1 The contradiction is in certain respects not absolute. Nordhausen took leaves of Mnium , 
laid them on the surface of a nutrient jelly, and sprayed Botrytis spores over the upper surface. 
The spores grew down into the cells of the leaf, being attracted chemotropically by the nutrient 
passing up from the underlying layer of jelly. The moss cells were killed, their contents discoloured, 
and the cell cavities finally became filled with a mass of hyphae. On the last point it is difficult to 
see how any mistake could have arisen, and it may be that the absence of a special chemotropic 
factor in the experiments of the present paper may have been responsible for failure to produce 
infection. 
