Oct. 13, 1923 
A New Tumor of the Apricot 
49 
Little need be said about the tissues lying beneath the periderm. The 
phloem, the next internal tissue, is traversed through nearly all its length 
by the medullary rays, which radiate also through the next tissue, the 
xylem or wood, and terminate internally in the pith in the center of the 
tree. The phloem and xylem are separated by the cambium; a single 
layer of meristematic cells, which, by constant division and subdivision*, 
in a radial direction, deposit wood toward the interior and phloem tissue 
toward the exterior. 
PATHOLOGICAL HISTOLOGV 
On the outside of the gall remains of the epidermis may be found still 
attached and, beneath, the periderm with its cork strata alternating 
occasionally with more or less incomplete strata of phelloderm or cork 
parenchyma and clusters of sclerenchyma cells, in the same way as has 
been observed in the normal tissue of the Moorpark apricot. This is the 
original bark, which, under the diseased condition, has been dislocated 
from its normal position and pushed to the exterior. When, however, 
the region where the periderm ends and the phloem begins is reached, it 
is found that the two kinds of tissue are not sharply marked off as 
they are in the normal condition, but, instead, strands of cork tissue are 
found diverging from the normal parallel course and forking off to enter 
tlie phloem. Strands of cork tissue have been observed leaving the 
periderm and penetrating into the phloem region, incidentally crossing the 
medullary rays and occasionally abutting into the cambium. Plate 6 
shows cork tissue deep in the phloem. Note the strands of cork tissue 
at A and B close to the cambium. Plate 7 shows cork and phloem 
tissues grown into each other. Note the cork strands at A, B, and C, 
and the medullary ray D, whose course is obstructed by the cork. 
Another pathological feature illustrated by this plate is the unusual 
abundance of sclerenchyma cells in this region (E). 
The presence of cork in the midst of phloem tissue—the actual min¬ 
gling of two kinds of tissue in a more or less complicated manner often 
resulting in portions of the phloem being surrounded on all sides by 
cork—constitutes the most striking feature of the pathological histology 
of the gall tissue. This condition is characteristic of all the tumor 
growth lying outside of the line which is continuous with the normal 
bast (PI. 3, B). 
The cork becomes less and less abundant farther inward. The phloem 
lying immediately outside of the wood, although occasionally invaded 
by strands of cork tissue, is soon replaced by new phloem formed by the 
cambium, and the disorganized bast is pushed to the exterior. 
The surrounding of phloem tissue on all sides by strata of cork cells 
several layers deep would in itself be sufficient to result in the death 
of the inclosed tissue, for cork, being impervious to water, prevents the 
interchange of nutrients in solution through it. The inclosed tissues 
would thus be expected to die of starvation. 4 While this may actually 
be taking place in the tumor, it is generally found that the tissues itt the 
region under consideration are in a much more advanced state of dis¬ 
organization than can be attributed to the effects of starvation. The 
4 This is what happens normally in the old bark of the oak and elm—for example, where layers of phloem 
are cut off from water and food supply by deep layers of cork tissue. The isolated phloem tissue soon dies 
and, together with the cork, becomes furrowed by many clefts and fissures. So it happens in the case 
of the grapevine and birch, where the dead phloem and surrounding cork slough away after drying. 
