Nov. 29,1915 
Varietal Resistance of Plums to Brown-Rot 
377 - 
Lying below the hypodermal layers of cells and in sharp contrast 
to them are the large, isodiametric cells which make up the mass of the 
fruit tissue (PI. XXXVII, fig. 6). In the ripening process in those varie¬ 
ties which become soft these cells split apart at the middle lamella 
(PI. XXXVII, fig. 5). The solution of the middle lamella apparently 
takes place more readily in these cells than in those of the hypodermal 
layers. 
METHOD OP ENTRANCE OF THE FUNGUS 
Two methods were used in the determination of the details of the 
entrance of the fungus. The first consisted of macroscopic observations 
on ripe or nearly ripe fruit shortly after infection had taken place. 
In the second method fruits of a number of varieties of plums at various 
stages of development were brought into the laboratory and inoculated t 
in some cases by a suspension of spores in water and in others by laying 
the plums in contact with moist mummies well covered with spores. 
After infection had taken place and small decayed spots had appeared, 
blocks of the ilesh, including these spots, were killed and embedded in 
paraffin, according to the usual methods employed. These were later 
sectioned, mounted, and stained. Sections 8 to njn thick were found 
most satisfactory. Various stains were used, including Harper’s short 
modification of the triple stain, Heidenhain’s iron-alum-hematoxylin, 
and also a modification of this in which safranin was used. This last- 
named stain proved very satisfactory. 
It was noticed continually, particularly in ripe or nearly ripe fruit, 
that when infection took place through the uninjured skin, the spot always 
had in its center a lenticel or “dot.” These observations indicated that 
infection takes place, not through the cuticle, but through the lenticel in 
ripe or nearly ripe fruit. Further evidence was obtained on this point 
when sections were made of the skin from material in which the lenticels 
were either forming or completely formed and through which infection 
had taken place. It was found that the hyphse entered between the 
guard cells into the stomatal cavity (PI. XXXVIII, fig. 3, 4, and 5). In 
those stomata lined with corky material infection of the fruit tissue does 
not take place immediately, as the fungus apparently has not the power 
to pierce directly through the corky cells. The hyphae continue to grow, 
filling up the stomatal cavity, and eventually exert enough pressure to 
split away the epidermis from the lenticel cells (PI. XXXVIII, fig. 5). 
It is through this opening that infection takes place into the fruit tissue 
(PI. XXXVIII, fig. 1 and 2). 
In the young plums, before corky material has been formed, the germ 
tubes also enter through the stomata. Aiter entering they come in contact 
with normal fruit tissue, and direct infection takes place (PI. XXXVIII, 
fig. 4). In all, 44 instances of infection through stomata or lenticels were 
noted, and although the surface of both ripe and green plums was often 
