THE MOSAIC DISEASE OF CUCURBITS. 9 
mottling of yellowish green. Such plants seldom produce fruit and 
are usually short lived, rarely reaching a length of more than 1 2 inches. 
Symptoms on plants infected when young. — The period of most 
general infection begins when the plants are about 6 weeks old and 
growing vigorously. At this time they have from six to eight leaves 
and are commencing to run. The first symptoms in all cases appear 
in the young leaves which are still in the process of development and 
usually are not easily recognized by an untrained observer. The 
youngest of the leaves develop small greenish yellow areas, often not 
more than a millimeter or two in diameter, occasionally circular, but 
more often limited in outline by the smaller veins of the leaf. These 
spots are slightly more translucent than the remainder of the leaf and 
are often scarcely visible except by transmitted light. Less commonly 
the normal green of the leaf changes to a peculiar yellow at the tip 
and the sharply defined yellow areas do not appear. Accompanying 
these symptoms there is a gradual downward curling of the edges of 
the leaf, and the surface presents a finely wrinkled appearance, the 
tissue between the small veins becoming slightly raised so as to form 
minute convex surfaces (PI. I, B.) Following these early symptoms, 
the gross mosaic characters develop rapidly, and the leaves become 
strikingly mottled with green and yellow. Such leaves are wrinkled 
and savoyed in appearance and may be somewhat distorted and 
curled (PI. II, A). 
All growth subsequent to infection is mucn dwarfed, the stem 
internodes are shortened, the leaves attain only about one-half nor- 
mal size, and the petioles are reduced in length. As the plant be- 
comes older the wrinkled and savoyed character of the leaf is more 
marked, but the mottling is generally less conspicuous. 
Plants infected at this stage blossom sparingly and set few fruits. 
They send out few runners and have a bunched and bushy habit of 
growth, with the leaves lying close tcr the ground in a rosettelike 
clump. 
Symptoms on plants infected when nearly mature. — In the case of 
large plants the general symptoms are similar to those described 
above. The first signs of the disease appear in the youngest leaves, 
where the yellowing and curling before noted are the usual indica- 
tions of infection, while all the older leaves appear normal and may 
remain so for some time. In some cases, however, the youngest 
leaves turn yellow and wilt, their edges becoming brown and withered, 
and all the leaves of a shoot may thus wilt within a few days. Ordi- 
narily, however, only three or four leaves at the growing point are 
affected in this way, and the runner soon sends out a new shoot just 
back of the withered tip, which shows the ordinary mosaic symptoms. 
Symptoms may also appear very early on the young fruits, and in the 
first stages of the disease they are often more marked than those which 
occur on the leaves (PI. II, B). Frequently the most pronounced 
