142 



walls are thin and without pores, and consist, particularly the 

 longitudinal walls, of lamellae of cellulose and cellulose-mucilage. 

 The mucilaginous character of the wall may be readily detected 

 in glycerin mounts of sections of material previously treated with 

 alcoholic solution of methylene blue. 



Usually between the sixth and eighth internodes from the top 

 of the stem certain changes are observed in the character of the 

 central pith cells. Some of the cells become more or less rounded 

 in outline and appear to lose a part of their organized contents. 

 The intercellular spaces become larger and with the subsequent 

 breaking down of some of the cell walls, as well as the collapsing 

 of some of the cells, large biconvex cavities are produced at 

 quite regular intervals and extending to the lowest internode. 

 These chambers are from one third to two thirds the width of 

 the stem, and are from i to 4 mm. in depth. Separating these 

 cavities are biconcave diaphragms consisting of cells similar to 

 the other pith cells, only they contain small masses of mucilage 

 and considerable protein matter, and in some of the cells the sap 

 is replaced by air, giving the diaphragms a white appearance. 



We have thus in Phytolacca decandra a pith differentiated into 

 two parts, a peripheral portion made up of active cells, as already 

 described, and a central portion consisting of biconcave dia- 

 phragms composed of both active and inactive cells, separated at 

 regular intervals by cavities. The latter appear to be formed by 

 the abstraction of water from the cells of this region as a result 

 of the development of other parts of the stem. This view seems 

 to be confirmed by the fact that in the process of drying that 

 portion of the pith in the upper internodes, which is not already 

 metamorphosed, becomes thus differentiated. 



The central pith somewhat resembles the pith of certain 

 xerophytic Compositae, and while the chambers might be looked 

 upon as latent or neglected water reservoirs, still they do not 

 seem to have this function. 



The metamorphosed pith in Phytolacca decandra seems, on the 

 one hand, to have a certain resemblance in origin to the hollow 

 internodes of the stems of the 'Polygonaceae, and on the other 

 hand to resemble the heterogeneous or modified pith of the 



