404 MANUAL OF FRUIT DISEASES 
attention. Once affected, the plant continues to show signs 
of yellows annually to some extent. Cases are on record where 
recurrence of the disease has taken place for nine consecutive 
years. , 
Both healthy and diseased raspberry plants may occur in the 
same stool. In extended outbreaks all gradations between 
healthy and affected plants obtain. One of the more striking 
symptoms of yellows is that the plants are stunted, sickly and 
bushy in aspect (Fig. 118). In general the condition recalls 
that of peach-yellows. The fruit-bearing laterals are dwarfed, 
often being but one-half their normal length. The leaves 
themselves present an unmistakable characteristic when affected 
with yellows (Fig. 118). They are abnormally small, and the 
margins of the upper leaves curl downward (Fig. 118). The 
tissue between the leaf-veins arches upward, and as a result the 
veins appear sunken. This uneven growth brings about a 
curling of the foliage (Fig. 118). In summer, the foliage ac- 
quires a mottled appearance (Fig. 118); at first a light colora- 
tion prevails, then it gradually changes to a darker green and 
yellow, and finally is reddish bronze. The colorations accom- 
panying and symptomatic of yellows vary considerably with 
the soil and climatic conditions. The disease is more conspic- 
uous in dry and hot weather. The berries on diseased plants 
usually become dry before maturity, or they ripen ten to four- 
teen days early. In case they dry up, the change may be 
gradual or sudden. If the fruit ripens prematurely, it is bitter, 
lighter in color, and smaller than normal. Not uncommonly 
the flowers develop prematurely on the tip of the current year’s 
growth. From all appearances the root-system is normal. 
Cause. 
As yet the causal nature of raspberry-vellows is unknown. 
Various factors have been assigned in this connection, but 
always without proof. Among these may be noted fungi, 
insects, bacteria, poor drainage, lack of soil fertility and other 
