20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



shoots may be somewhat faded and yellow. The yellow coloration may 

 be total or partial, and the leaves irregularly dry in those parts of the 

 parenchyma longest deprived of chlorophyll, that is from the edges 

 inward. The lower leaves are more affected than the upper. 



Following the shriveling of the grapes, the foliage of the more vigor- 

 ous vines, after a longer or shorter time, begins to show the same char- 

 acters that the leaves of the weaker vines assume at an earlier period. 

 These characteristics are illustrated in the accompanying colored 

 figures on Plate I. The chlorophyll becomes resorbed at the edge of 

 the leaf (Plate I, Fig. 7), which yellows; this resorption may continue 

 until the whole of the leaf is bright yellow (Plate I, Fig. 1). 

 Following this stage, which is not infrequent in the basal leaves, the 

 leaf either dries up completely and at once (Plate I, Fig. 3), or, as occurs 

 more often, from the periphery inward, with a slight rolling of the edges 

 (Plate I, Fig. 2). In other cases, however, the entire blade of the leaf 

 does not become so regularly yellow and then dry. Indeed, one fre- 

 quently observes the yellowing at first confined to the apical lobe (Plate 

 I, Fig. 4), and then gradually progressing toward the petiole (Plate I, 

 Fig. 5), the wings of the leaf remaining the while of a sub-healthy green. 

 The chlorotic tissue gradually dries, sometimes irregularly, but not 

 infrequently in a very regular manner (Plate I, Fig. 6). As soon as 

 the center portion of the leaf has dried, the wings of the leaf die. Fig. 6 

 represents a leaf, the center of which became chlorotic and then dried 

 up; the death of the entire leaf then followed. 



A leaf presenting the characters of that illustrated in Fig. 8 is more 

 exceptional. In this leaf the greater part of the leaf-blade was sud- 

 denly killed without previous yellowing or chlorophyll resorption. The 

 dead tissue, it will be observed, has a shade of green in it, whereas in 

 all the other diseased leaves it is fawn-colored or brown. If the reader 

 will imagine the dead tissue (Fig. 8) colored brown instead of greenish- 

 fawn, he will have the representative of a leaf that was chlorotic around 

 the edges and in the greater part of the blade. This chlorosis, however, 

 did not spread, and the affected tissue rapidly died without impairing 

 the functions of the remaining healthy portion of the leaf. 



Internal Appearance of the Shoots, Spurs, Arms, and Body of Vines. 

 The spurs, the arms, and the body of the vine show no outward signs of 

 disease at all. The shoots mature sometimes very unevenly, but this 

 characteristic is unimportant. The shoots, spurs, and body of the vine 

 show, however, certain internal symptoms which should be noted. 



Cross and longitudinal sections of the shoots, spurs, arms, and body 

 of the vine show discolorations in the wood and pith. In the shoots a 

 slight discoloration of the woody tissue next the pith can be traced with 

 comparative ease at least as far as the last bunch of grapes showing 

 shriveling; but the brown discolorations in the pith are not so constant: 



