Bark Canker Disease of Apple Trees. Grace G. Gilchrist. 23% 
them as long, cylindrical, hyaline, perfectly characteristic of 
the genus Myxosporium. 
In nutrient solution, the spores germinated readily, a germ 
tube being put out during the first day, generally near one end 
of the spore. During the second day the spores usually became 
I—3-septate and of a decidedly brownish tinge and later other 
germ tubes developed. After germination the mycelium grew 
very slowly, only producing a colony about 3 mm. in diameter 
in two weeks. Edgerton did not succeed in obtaining spores in 
artificial culture. 
Lewis(z) in Ig12 isolated the species from diseased apple 
branches. He transferred the fungus from plates to bean pods 
where it fruited and produced spores identical in shape and size 
with those from pustules on apple branches. Inoculation experi- 
ments which were carried out were not satisfactory and Lewis 
came to the conclusion that Myxosporium is not the sole cause 
of the killing back but that it attacks weakened branches, 
hastening their death and giving the appearance that they had 
been killed by a more active parasite than this fungus seems 
to be. 
Stewart, Rolfs and Hall(3) in 1900 referred to this fungus as 
Macrophoma Malorum (Berk.) Berl. and Vogl. The opinion had 
previously been advanced that Macrophoma Malorum was an 
immature stage of Sphaeropsis Malorum Peck, but Stewart and 
his associates believe that the two forms are distinct. Subse- 
quently (1910) Stewart accepted Edgerton’s(z) name. 
Hesler and Whetzel(4) in 1917 included a brief description of 
the disease in their Manual of Fruit Diseases. They state that 
the fungus is confined to the cortex, and that the originally 
infected areas are small and more or less circular, but larger 
cankers of various shapes finally appear as the result of the 
coalescence of two or more cankers, but that the fungus is 
responsible for such slight damage that it is very doubtful 
whether any sort of remedial measures are ever necessary or 
profitable. 
GENERAL APPEARANCE OF THE DISEASE. 
The most characteristic feature of the bark canker disease is 
the extremely long narrow scars which it produces. These may 
run for a length of two or three feet down one side of a stem 
and not reach a breadth of more than 14 inches. The disease 
may start at the top of one of the main branches and grow 
downwards, or it may develop from the soil level infecting the 
trunk and causing the rapid death of the tree. The dead area 
of the scar is somewhat sunken below the surrounding tissue 
owing to lack of new growth. The edges of the scar are usually 
