10 BULLETIN 879, TJ. S. DEPARTMENT OF AGEICULTUBE. 
leaf symptoms appear on new secondar} T shoots put out from the 
axils of the leaves near the base of the plants. The wilt symptoms 
are often noted on tlie cucumber and pumpkin and occasionally on 
the Summer Crookneck squash and muskmelon. 
In the greenhouse this type of response is much more intense, 
and it is common to have the vine suddenly develop a yellowing and 
wilting, which extends to the entire plant within two to three days, 
the older leaves usually showing yellowing but wilting very rapidly. 
This wilting and death of the plant occur only occasionally in the 
field and never progress so rapidly there as they do in the greenhouse. 
Aside from these differences, the older plants in the field show the 
same symptoms as plants infected at an earlier stage in their devel- 
opment. The dwarfing and wrinkling of the younger leaves are very 
pronounced and the mottling is of the same type as that on younger 
plants. The shortening of the stem internodes and the petioles 
gives the runners a flattened appearance, and the leaves lie close 
to the ground. 
The older leaves of mature plants are later more severely affected, 
and the greater portion gradually die off. Portions of the leaf turn 
yellow, those at the base of the stem being affected first. This may 
occur as a gradual yellowing of the entire leaf, or more characteris- 
tically as a V-shaped yellowed area along one of the large lateral 
veins of one of the basal lobes. The tissues of these yellowed portions 
rapidly turn brown and die, beginning at the edges in the angle formed 
by the lobes and working toward the base of the lateral veins. (PL 
III.) The entire leaf eventually becomes yellow, this yellowing grad- 
ually extending to the leaves farther up the stem. Such leaves 
finally wither and die, leaving the basal portion of the stem bare. 
This is a characteristic symptom in late stages of the disease, and by 
the end of the season many plants show 1 to 3 or more feet of bare 
stem with the dead leaves still attached, but terminating in a cluster 
of dwarfed, dark-green, mottled, and wrinkled leaves which lie 
close to the ground. (PL II, C.) 
LEAF SYMPTOMS. 
The pattern of coloring which the leaves of mosaic plants assume 
varies with the species, the age of the plant at the time of infection, 
and the stage of development of the individual leaves. 
Leaf symptoms on cucumbers. — On the cucumber (Cucumis sativus) 
the mosaic mottling is usually most pronounced and typical on the 
young leaves of plants which are growing rapidly (PL IV, A) . The 
green portions of these leaves are very dark in color and are raised 
slightly above the surrounding surface, thus giving the leaf its savoyed 
appearance. In most cases the green areas predominate, being 
intermingled with spots of light greenish yellow. These yellow spots 
are irregular in outline and are limited by the small veins (PL IV, B). 
