ANTHRACNOSE OF CUCURBITS. 29 
petioles the intracellular mycelium about the advancing edges of the 
lesion is easily seen without staining. 
As to the effect on host cells besides the shrinkage and the staining 
reaction above noted, there appears to be an enlargement of the host 
nucleus, often followed by its division (figs. 6 and 7) and in some 
cases by cell division (fig. 11). In cucumber-stem lesions there seems 
to be a tendency toward callus formation. 
To sum up, it may be said that the mycelium is intracellular and 
that shrinkage and collapse of the invaded host cells occur. There 
are indications of a stimulus to cell division. 
LIFE HISTORY OF THE CAUSAL ORGANISM IN RELATION TO THE DISEASE. 
SEASONAL DEVELOPMENT. 
Previous observations indicate that anthracnose is a disease 
which becomes serious only rather late in the growing season of its 
host. Observations made 
during the course of this 
work lead to the same con- 
clusion. This appears to be 
due to the mode of origin 
of the disease in rather iso- 
lated and restricted cen- 
ters in each field, from 
which subsequent spread, 
dependent upon heavy 
rains, is rather slow until 
a considerable reservoir of 
infection has developed. 
The strict relation of epl- Fig. 11.—Cross section of a leaf lesion 121 hours after inocula- 
demics of this disease to tion. Appressoriumshown. Mycelium intracellular, The 
: division of invaded palisade cells and collapse of epidermal 
wet weather is well r €COZ- and _palisade cells are visible. (Camera-lucida drawing; 
nized in the literature (41, ™2guified about 570 times.) 
43, 44), and the importance of climatic conditions can not be over- 
estimated. 
DEVELOPMENT IN 1915. 
Observations upon the disease as it occurs among cucumbers were 
made during the summers of 1915, 1916, and 1917. The summer 
of 1915 was cool with frequent and abundant rainfall. At Prince- 
ton, Wis., the disease was first noted in a 2-acre experimental field 
on July 14. This infection was confined to lesions on the first and 
second leaves of two adjacent plants planted seven weeks previously. 
The next day the disease was found in a neighboring private field. 
By July 20 several centers of anthracnose were noted in the latter 
field. On July 21 anthracnose was found in another private field 
in town. 
