42 
EIGHTH REPORT. 
lulose ill the cell walls of the apple, is an adaption favorable to the 
fungus in tiding it over from time to time, or from season to season. 
This inference is furthjer supported by the fact that in such mummy 
apples no perithecia are produced. Perithecia are common enough in 
affected crab apples, but in these there is very little development of 
cellulose in the cell walls as compared with common apples so affected. 
This is partly true also with respect to the formation of starch, for 
there is much less to be found in apples in which the perithecia are 
developed, than in those in which they are not. 
Upon examination of affected fruit from time to time after inocula¬ 
tion with black rot, it may be seen that, as the cell walls become 
thickened, the quantity of starch grains become lessened. This cell- 
wall thickening takes place from without, proceeding towards the cen¬ 
ter, until practically the whole liquid content of the cells of the fruit 
is changed into solid. A section perpendicular to the surface of an 
apple, well on towards mummification, shows the cells at the outside to 
possess walls ten to twenty times as thick as in the unaffected apple, 
and the cell-content a small mass shrivelled up and with almost no 
liquid. These cells contain occasionally a starch grain or two. The 
cells which are about thirty cells deep from the surface of the apple, 
possess walls two or three times as thick as in the unaffected apple, 
and quite large quantities of starch grains, in some cases as many as 
forty or fifty grains in a cell, with some other solid content and some 
liquid. The cells between those two extremes, shade off with regard 
particularly to cell wall thickening, number of starch grains in a cell, 
other solid cell-content, and to liquid cell-content. 
1 he mycelium of the black rot is intercellular, as a rule, but occa¬ 
sionally it enters the cells, not, however, by producing regular haus- 
ioria, but by means of the ordinary mycelium which sometimes not 
only enters the cells but also passes right through them. In the 
enormously thickened walls, the mycelium may readily be seen, espec¬ 
ially if the section be stained, branching all through the cellulose. The 
character of this' mycelium is thin-walled with liyphae of verv small 
diameter. Occasionally a strand of the mycelium is rather large, but 
these large strands occur mainly between the cells and where wall 
thickening has not proceeded to so large an extent. This large mycelium 
is sometimes found near the surface, but in such cases it grows right 
through the cells, penetrating the walls on both sides. This has more 
numerous septa, than the finer hyphae which ramify so profusely through 
the cellulose. 
The black coloring of the affected apple is due mainly to the char¬ 
acter of the cell contents of the outer layer of the cells’ The content 
of these cells is very dense in color. The mycelium of the fungus in 
the region of this layer of cells is slightly dark in color, while that 
penetrating the tissue of the apple farther in, is colorless. (The mycel¬ 
ium is colorless on culture media.) 
In the crab apple, where perthecia are formed, the mycelium is often 
almost black in color, especially that portion in the body of, and 
around, the perithecia. But the mycelium does not destroy the fruit 
as stated by Tubeuf and Smith* but actually seems to act as a sort 
in co T ntquLcfbocome s P drted “ d diStr0y6S the Skta ° f the frUit ' which ' 
