408 BOTANICAL GAZETTE [May 
tube had entered. This must have been due to a toxin freed during the ger- 
mination. The author investigated this further and proved that it was a very 
vigorous substance. The browning of the cell walls precedes death of the 
protoplasm, The author concludes, from what seems to be ample evidence, 
that there are two substances produced, an enzyme that browns the wall and 
digests it, thus producing a soluble substance which attracts the germ tube 
chemotropically. Later there is a toxin which kills the cell and this affords 
the fungus a base of supplies for a saprophytic existence. Thereafter it may 
easily invade surrounding tissues to any extent. Slight humidity favors 
germination of the spore, but great dampness dilutes the toxin and enzyme; 
therefore the optimum destruction is at a moderate humidity. The author 
olds that, even in the case of subepidermal wounds or the hypodermic 
injection of sugar (Miyoshi), the fungus does not attack live cells, but its 
Saprophytic existence is thus assured while it liberates its toxin; it is also 
possibly aided by weakening of the resistance of the cell through the unnatural 
conditions. Many suggestions are made regarding the influence of the con- 
dition of the host upon resistance ; among them, that normal structure counts 
for much (e. g., thick epidermis) ; growing portions are susceptible because 
thin walled ; similarly, great dryness weakens the resistance of the ectoplasm, 
and lack of light results in a thin wall, etc. The author attributes epidemics 
largely to climatic conditions, or to a breeding place for the fungus wae e 
may obtain food for its existence as a saprophyte. He explains that in such 
times any particular host species succumbs probably because it furnishes a 
foothold in some way for a temporary saprophytic existence of the parasite. 
Or, a given plant may through its own specific heat cause an exactly favor- 
able amount of dew to be condensed on its surface. : 
Two more questions are investigated, viz.: Can a representative pure 
saprophyte (e. ¢., Penicillium, Mucor) under tain liti I ete ea 
site? Why are they so seldom parasitic ? The first is answered abundantly 
in the affirmative (e. g., fruit decay). Why they are not often parasites !S 
shown by the fact that they cannot penetrate a live cell, even of the mG 
phyll, although they can penetrate cell walls and may live among the ‘ 
Host cells may even live for sometime in contact with the mycelium. . 
Seems, therefore, that these fungi make no toxin, as do the oo . ; 
hemisaprophytes. In the case of wounds the reaction of the plant is ion re : 
The host may set to forming parenchyma; then the advance of the ott is 
will depend upon how much it can hinder this recuperative process. 
yay ictori- 
fight to thedeath between the host and the fungus. Botrytis 1s usually vic “s 
t upon t 
amount of resistance of the host. In the case of sapro 
resistance is more important, as the fight is waged in every cell anew, 
4 : ; : ey: 
even such fungi, fruits are so slightly resistant as to be an easy PT 
