OBSERVATIONS ON SOME VINE DISEASES IN SONOMA COUNTY. 7 



leaves, which are naturally yellowish-green, this discoloration is more 

 indicative of the disease than the change in color. Following the loss of 

 color, the leaves become somewhat convex and the edges curl toward 

 the lower surface; they lose their natural appearance; the tissue 

 between the main veins sinks, and the veins themselves stand out like 

 ribs. In mild cases the disease may develop no further than this. The 

 affected leaves, however, fall off sooner or later, and generally with 

 their stalks (petioles). 



In severe cases of the disease, the recently expanded leaves may dry 

 up suddenly and totally without malformation of any kind; or, as 

 occurs more frequently, the parenchyma becomes pale yellowish-green, 

 and the inclosed network of small veins discolored; then, usually, the 

 lobe, or at least the upper portion of it, or in entire leaves that portion 

 of the parenchyma which occupies the equivalent position, including 

 one wing of the petiolary sinus, becomes more or less convex and the 

 tissue sunken between the veins, which stand out, often in bold relief. 



At this stage the tissues begin to dry rapidly from the periphery toward the petiole, 

 at the same time retaining their peculiarity of form. When dry, the tissues are brittle 

 and reddish brown. As soon as the discoloration has reached the petiole, the entire 

 leaf and leaf-stalk may fall together. In older leaves, those not yet fully developed and 

 still growing, one observes great variations variations which can not be accounted for 

 by the position of the leaf in relation to other diseased leaves, or by its age. Some leaves 

 show the characteristics just described as typical of recently expanded ones, except 

 that they do not fall prior to the dying of the convex and furrowed area. The drying 

 of that portion of the leaf proceeds as rapidly in one case as in the other. In the more 

 fully developed leaves, however, the action is sufficiently striking. At the petiole, and 

 in the region immediately adjoining it, the mid-rib serves as a line of demarkation 

 between the living and the dead tissues. The dead tissue soon separates from the 

 petiole, which, in turn, discolors. At this stage the leaf-blade separates from the petiole, 

 which, though drying up and discoloring more or less from the apex down, remains a 

 while longer attached to the shoot. In other cases, besides the dead and furrowed area, 

 there may appear between the veins, on other parts of the leaf, spots which, at first yel- 

 lowish, become, at the same time as the aforementioned area, dry and reddish-brown 

 in color, except for a narrow margin next to the still green or greenish-yellow tissue. 

 Or again, the leaves may present the following appearance: The leaf-tissue, while still 

 green, becomes sunken between the veins; then, in one or sometimes both corners, the 

 leaf becomes pale greenish-yellow and between the veins, in the remainder of the leaf, 

 appear spots of various sizes of the same color. These spots enlarge and even run 

 together to form stripes. At this stage the discolored areas begin to dry rapidly, assum- 

 ing the familiar reddish-brown color. The tissues next the petiolary sinus rapidly dry 

 up from the periphery inwards, but do not encroach upon the mid-rib, and one may 

 sometimes find a leaf which still adheres to its stalk, after the parenchyma on each 

 side has become detached. A slight margin of yellow T ish-green sometimes separates the 

 dead furrowed area from the still living tissues; this margin of yellow is, however, 

 generally more distinct around the spots and stripes of dead tissue in the other parts of 

 the parenchyma. The leaves fall from the petioles, which soon follow r them. 



In fully-developed leaves and old leaves, the disease is not accom- 

 panied by any distortion or furrowing of the leaf-blade. It affects only 

 the tissues between the main veins, and first appears as suffused green- 

 ish-yellow spots, which, at first indefinite, become gradually larger and 

 more definite in outline, and often merge together, forming large macu- 



