STRUCTURE.] FORMS OF BOTHRENCHYM. 57 



full of holes. Upon a more accurate inspection, however, it 

 is found to receive that appearance from its sides being filled 

 with little pits sunk in the thickness of their lining. (See 

 Plate II. fig. 2.) 



By far the most complete account which we possess of 

 this kind of structure, is due to the accurate researches of 

 Professor Mohl, whose remarks I quote at length from 

 Mr. Berkeley's translation in the Annals of Natural History, 

 vol. ix. After adverting to the mistake committed by some 

 anatomists in regarding the structure of pitted tissue as 

 being extremely uniform, he proceeds to describe various 

 very distinct forms. 



In the first instance, however, he points out the important 

 fact, that the pitted tubes of most plants do not possess an 

 uniform structure all round, but the condition of their walls is 

 materially affected by that of the contiguous organs. The 

 medullary rays in many plants exercise a powerful influence on 

 the structure of the cells of bothrenchym, as in those parts 

 of the tube which are in contact with the medullary rays the 

 pits have an irregular form, want the customary borders, are 

 always situated where only a neighbouring cell is closely 

 pressed, and near where the lateral walls of a neighbouring 

 cell stand perpendicular to them ; that, moreover, the pits of 

 two tubes applied immediately the one to the other exactly 

 correspond. 



The forms of Bothrenchym, recognised by Mohl, are the 

 following : 



A. Where the walls exhibit no variations, whether standing 

 in contact with other tubes or with cells, being therefore 

 uniformly studded with pits which are surrounded by a border, 

 as in Elseagnus acuminatus, Clematis Vitalba, Broussonetia 

 papyrifera. 



B. In which those sides of the tubes which stand in 

 contact with prosenchymatous cells are furnished with equal 

 dots surrounded by a border, but in which the action of 

 neighbouring cells is indicated by the pits on the walls which 

 abut on the cells being placed at greater distances. Such 

 tissue occurs in Bixa Orellana, Acacia lophantha, Sophora 

 Japonica. 



