138 . OBSERVATIONS ON THE CALIFORNIA VINE DISEASE 
pass the starch in a brown translucent film. Where the medul- 
lary rays begin, and in the secondary wood, this occluding matter 
is darker; the starch grains are blackened, or appear to lie in a 
blackish matrix, or the lumen of the cells may be filled with a 
homogeneous black mass. Sometimes before the medullary rays 
reach the cortex the following change takes place: the starch 
has largely disappeared from the cells, and the brown irregular 
lining of their walls appears to be due to an incrusting of the 
primordial utricle. In the cortex the medullary rays present the 
following appearance: the lumen of the cells is more or less 
filled with yellowish or brown homogeneous matter. The deposits 
are darker where the bast fibers have not been produced. Brown 
homogeneous matter occludes the greater number of the phloem 
cells. The cells in the cortical parenchyma, collenchyma, and 
epidermis may also be more or less occluded. Thylloses are gen- 
erally present in the primary wood, and are not infrequently very 
numerous in the secondary wood; they contain now and then 
granuloids. The discoloration of the cell walls in the different 
tissues is, except, perhaps, in the neighborhood of the cambial 
layer, rather inconstant. 
Outside the immature spot the occlusion of the cells is less 
pronounced, though of the same general character. 
The matter occluding the cells in the diseased canes does not 
appear to differ, for the most part, from that filling the cells of 
the leaves. Microchemically, the gummous substance in the cells 
of the mesophyl does not differ from the occluding matter found 
in the cells of diseased canes. This statement, though generally 
true, needs to be qualified: the reactions characteristic of the 
deposits found in the leaf are more constant in the cortex, and 
especially in the phloem, than in the wood, in this latter tissue 
a great deal of browning of the primordial utricle seems to be 
due to death rather than to particular catabolic changes—hence 
the normal appearance of the starch. 
Roots.—The roots may be either healthy or show, without 
structural modification, to a lesser or greater degree, the same 
character of cell occlusion I described as occurring in the cells 
of diseased canes, less the accompanying starch when decay js. 
evident. | 
