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 O18 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 sin-face. 



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. 



