Spur Blight of the Red Raspberry 
15 
m 
shows the change in the color of the deep layers, in passing from 
healthy to diseased tissue. From A to C the cane was normal and 
green in color; the outside cortex was removed from B to D; from 
B to C the inside cortex was white; from C to D it was brown; 
from D to E the cane was brown. This discoloration appears to 
the naked eye to extend no deeper than the 
cortex, but a microscopic examination of a 
section shows that this is not altogether 
correct. 
The cells of the entire cortical layer, from 
the epidermis to the phloem, are badly 
shrunken and present a brown shriveled aspect 
characteristic of dead, collapsed tissue. Many of 
the phloem elements, as well as the cells of the 
medullary rays show an accumulation of food 
material greater than that of corresponding 
cells of normal tissue. While these cells ap¬ 
pear amber brown in color, they are perfect in 
outline and in general structure, and do not 
suggest a fungous invasion. The brown color 
which they exhibit is traceable, in all proba¬ 
bility, to the excessive food material which has 
been deflected to these regions as a result of 
the enzymotic influence, exerted by the fungus 
which has invaded and destroyed the adjoining 
Figure s. cortical layer. The strengthening tissue (ster- 
eome), wood (xylem), and pith (medulla) exhibit no pathalogical 
condition. 
The Causal Organism. 
A microscopic examination of the brown cortical tissue shows 
it to be permeated with the mycelium of a fungus. This fungus 
has been isolated repeatedly with little difficulty from such material 
and has been grown for more than three years upon standard 
A BCD E 
Figure 9. 
