294 
and brown or reddish brown beneath. In abundance they 
range from afew on each leaf to such numbers as to be- 
come confluent and cover nearly the whole surface. After 
a time a pustule forms at the center of each spot beneath, 
which becomes clearly noticeable, especially under a lens, 
is pale yellowish brown in color, and when mature dis- 
charges a considerable mass of whitish spores. The spores. 
. being agglutinated, sometimes form 
tendril-like threads, but more often 
spread out into irregular masses, or 
are washed down by rain into a white 
ffilm. In August and September the 
quantity of spores produced on the 
under surface of plum leaves is often 
so abundant as to be clearly apparent 
to the naked eye. The form of the 
spores, as seen under the microscope, 
4 is given in Fig. 6; Fig. 7 shows a 
of _ verticle section through a pustule, 
che aL % Baera from which the spores have been 
loaves in Aucast. Moen, largely removed to give a better view 
fied 430 diameters. Orig- Of the manner in which they arise 
inal. ~ from the fertile layer of vertical 
threads. 
The primary injury which the fungus does the plum tree 
is twofold; it robs the tree of nourishment diverted to 


Big. 7.—Vertical section of a plum leaf bearing a septoria pustule, from 
which the spores are escaping. The discoloration of the tissues of the 
leaf by the fungus extends to the opposite surface, and joins the healthy 
tissues on the right in a well marked line. Magnified 150 diameters. 
Original. 
