MICHIGAN ACADEMY OF SCIENCE. 
41 
considered that fungi which work on stored apples are pro tcmto sapro¬ 
phytic, because the apple (the seeds excepted) was regarded as a non¬ 
living body. 
The black rot in a week or ten days after inoculation produces in 
the apple enormously thickened cell walls, and this thickening goes on 
until the whole fruit becomes mummified and dry. To the unaided 
eye the apple then has on its surface an ebony-like appearance. Sec¬ 
tions show thickened walls and starch grains in the cells. (It should 
be said that starch, though occasionally found in stored, ripe apples, 
is not generally present.) In the specimen here examined, care was 
taken to select such apples as possessed no starch, for inoculation pur¬ 
poses. Most of the cell contents of the apple had apparently disap¬ 
peared. The liquid content seemed to be the portion which had gone to 
build up cellulose and to produce starch. But this conclusion is 
mainly inference, drawn from the appearance of the cells afterwards, 
and from the fact that the apple shrivelled without apparently losing 
much water. Inoculated fruits were kept under different conditions 
in moist, atmosphere so as to see whether the shrivelling was wholly due 
to a mere drying out or to a change from liquid to solid within the 
tissue. A further corroborative test was made by injecting a strong 
fungicide within the apple to see if, when the fungus was killed, and 
certainly the contents of the apple cells also, the shrivelling action 
went on, to see if the process was a mere drying out process. This 
experiment supported the other tests, showing that it was not a mechan¬ 
ically drying out process. 
That many fungi produce an enzyme capable of dissolving cellulose 
is a matter of common knowledge. It is due to this dissolving ferment 
that fungus hyphae are able to bore through the mass of cellulose which 
constitutes the wall of the cell of the host plant. This cellulose wall is, 
as a rule, not quite uniform in its physical (perhaps chemical also) 
constitution. The portion first formed by the cell is usually more 
readily liquified or dissolved than is the remainder. When a potato 
or apple is boiled, the part first formed (middle lamellae) is dis¬ 
solved away and the cells become separated from one another. When 
tissue is macerated a similar condition results. An apple decomposed 
by a fungus has its cells separated similarly. The middle lamellae are 
dissolved away by the hyphae penetrating the tissue. It is quite largely 
due to the fact that the middle lamella is more soluble in the presence 
of the enzyme accompanying the fungus mycelium, that fungus mvcelia 
grow most frequently between the cells rather than into them, al¬ 
though the latter method would seem at first sight to be infinitely easier. 
This middle lamella has usually a different optical density from that 
of the other portions of the cell wall, hence it can generally be 
recognized, especially in lignified tissue, by examination with the micro¬ 
scope. 
The mummified apple, affected with the black rot, is practically in 
a state of preservation for an indefinite period, unless placed for a 
considerable time—a few days — in a moist place. If moisture be ap¬ 
plied, the mycelium commences to grow, and a portion of 
such mummified apple may then be used to inoculate other fruit. 
From this it might be inferred that the enormous development of cel- 
6 
