146 OBSERVATIONS ON THE CALIFORNIA VINE DISEASE 
spotted with dead tissue and dry up peripherally. Leaves that 
have ceased rapid growth or are already fully developed become 
yellowish green and more or less covered with maculations 
between the veins. The spots spread over the intervenium, not 
so much from individual development as from increase of 
centers. The centers of the maculations die, but a running to- 
gether of the dead areas to form stripes does not seem to pre- 
cede the death of the whole surrounding parenchyma. As a 
rule the leaves die from the edges inwards, and in severe cases 
maturation of the shoots is interfered with; the canes appear 
spotted or striped with immature tissue. The anatomy of patho- 
gnomonic leaves may be briefly described as follows: | 
A deposit, in the epidermal cells of the upper surface and, to a 
less extent, of the lower surface, occurs in the most diseased areas 
only. It is homogeneous to all intents and purposes, and rapidly 
thins out in the healthier cells. In the palisade tissue, where. 
the cells have not collapsed, they are either full of a homogeneous 
deposit or with granular matter. The chloroplasts are small, 
vacuolate, and scarce. The cells of the lacunose tissue in the row 
next the palisade layer, a certain number of them at least, con- 
tain disintegrated chloroplasts, but rarely globuloids. The re- 
maining cells contain disintegrated chloroplasts as well as granu- 
lar or homogeneous matter. The vessels of the small fibro-vas- | 
cular bundles are occluded, more or less, with granular Of 
homogeneous matter. The microchemical reactions of the de 
posits are the same as in the case of the California vine disease. 
| The disease is caused by Tetranychus Vitist and may be held 
. In check by sulphur or the polysulphides. 
We may conclude from the study of the relationships of the 
California vine disease that this malady, while having шапу 
ous of resemblance with other diseases, is, in diagnosing 
Specimens, likely to be confounded only with Folletage, Tetra- | 
nychosis or Sun-scald. I have just shown that all these disease — | 
have at least one salient character that differentiates them from — 
the California vine disease, and these characters are clearly. 
eg + Ў 
Мг. N. Banks, to whom I sent specimens for identification, could ва: e 
ға from the material at hand, whether this Tetranychus was T. Vitis я 
а n of T. telarius, but was of the opinion that it was T. Vitis Boisd : 
