28 WRIGHT : THE GENUS DIOSPYROS 
the same age are connected by the intervening parenchy¬ 
matous medullary ray cell, and a fairly continuous circum¬ 
ferential circulation of food materials can therefore be 
effected through such elements. In a few cases, however, 
the tangential line of parenchyma only reaches half way 
from one ray, the terminal cell appearing in transverse section 
to be surrounded by unlike elements ; it is conceivable that 
there may be some connection in the vertical course. 
In the majority of our species the tangential lines of 
parenchyma are only one cell in radial thickness ; in some 
species, notably D. affinis they are very often two, and are 
occasionally grouped in the middle of a patch of fibres. In 
some specimens of D. hirsuta the bands—two cells in radial 
thickness—often run together through a vertical distance of 
over 0*8 mm. These tangential bands of wood parenchyma 
are separated from one another radially by patches of fibres 
from 0*06 to 0*18 mm. in thickness. These elements are 
therefore in communication with like elements or those of 
the medullary ray by means of their radial surfaces, with 
fibres by their tangential surfaces, and with tracheal elements 
by any surface. 
The oblique bands of wood parenchyma are obvious in 
many species, and it is very probable that if sufficient 
material were examined they would be found to occur in all 
species. 
The components of these bands, instead of being arranged 
to form one line parallel to the circumference, are arranged 
in radial series, one slightly internal to the* next, and thus 
result in what may be described as a terraced system of 
parenchyma. Adjacent cells are usually in contact with one 
another by a part of their radial surfaces, and the terracing 
is therefore very gradual. Such systems of parenchyma 
connect one medullary ray to the next, but it is obvious that 
they tend to bring into direct communication the successive 
tangential bands between the same medullary rays, and 
therefore to establish a more thorough communication 
between like elements in tissues of different ages. 
