872 
Journal of Agricultural Research 
Vol. XXX, No. 9 
roughened buckskin areas on the fruit 
as described and illustrated by McKay 
(18, p. 181). Mosaic fruits are also 
characterized by more deep-seated 
lesions, producing an irregular pattern 
of hard, sunken, brown or black pock¬ 
marks, as shown in Plate 2, E and F. 
Ripening fruits often show rather ex¬ 
tensive sunken granular areas which 
fail to color properly and under which 
the seed pulp or placental matrix tends 
to remain greenish. 
Ovaries and very young fruits may 
show brown epidermal or deep-seated 
Fig. l.—Origin and development of the placental matrix in which the seeds in a tomato fruit are 
embedded. Camera lucida diagrams drawn to the same scale (X15) to show how the placental tissue grows 
out between and around the ovules, finally engulfing them completely, during a very short period early in 
the growth of the fruit 
A. —Locule of an ovary 3 mm. by 4 mm. in diameter showing ovules seated upon the surface of the 
axile placenta and completely filling the locular cavity 
B. —Locule of a small fruit 5 mm. by 6 mm. in diameter showing how the placental tissue has grown out 
between the ovules into contact with the pericarp, thus surrounding and separating the ovules and filling 
the locular cavity as the latter enlarges. The ovules are receding from contact with the pericarp 
C. —Portion of locule in fruit 7 mm. in diameter showing how the placental tissue has completely engulfed 
the seeds as the latter recede from actual contact with the pericarp. This placental tissue develops very 
rapidly and completely fills the enlarging locular cavity 
D. —Portion of locule in fruit 10 mm. in diameter showing distance to which pericarp has grown from the 
seed, the intervening space being filled by a cellular matrix resulting from the outgrowth of the placenta. 
It is in this placental matrix that the abnormalities predominate in mosaic fruits. The growth of pericarp 
and seed may also be noted 
EXPLANATORY LEGEND FOR PLATE 1 
A. —Section of pericarp through a surface blister such as is illustrated in B, showing the hyperplastic 
character of the blister tissue. The subepidermal cells have elongated and divided, pushing up the epi¬ 
dermis. If this tissue collapses the blister sinks and the epidermis usually cracks where it is sharply curved 
upward at the edge of the blister, thus forming the marginal fissure noted about the older lesions. Photo¬ 
micrograph X 33. Unstained 
B. —Surface blisters on a mosaic tomato 
U.—Section of a pericarp lesion resulting from necrosis and collapse of an area of subepidermal cells and 
hypertrophy of the cells immediately beneath the necrotic area. The necrotic surface of the underlying 
placental matrix, to which an ovule is adhering, is in turn adhering to the inner surface of the pericarp. 
Photomicrograph X 33. Stained with Haidenhain’s iron-alum haematoxylin. Fruit 12 mm. in diameter 
D. —Section of pericarp showing at the right a transverse necrotic plane accompanied by elongation of the 
near-by cells. At the left is a small necrotic spot in the pericarp. Photomicrograph X 33. Stained with 
carbol fuchsin. Fruit 12 mm. in diameter 
E. —Intumescences from a radial locule partition extending into an abnormal cavity which has resulted 
from the collapse of the necrotic placental tissue. Photomicrograph X 46. Unstained. Fruit 7 mm. in 
diameter 
