86 Prof. C. Morren on the discoid Piths of Plants, 



pletely exhausted, and remains a vehicle for air and reservoir of 

 excreted substances, henceforward of no use for vegetable life. 



EXPLANATION OF PLATE IL 



Fig. 1. Transverse section of the stem of a young Begonia argyrostigma. 

 A, B, C. Great grooves of the pith. 

 a, h, c. Small grooves of the pith. 

 Fig. 2. Vertical section of a similar stem. 



A. Node. 



B. Upper internode. 



C. Lower internode. 



a. Derm. 



b. Mesophloeum. 



c. Ligneous system. 



d. Nodal diaphragm. 



e. Pith. 



/. Slit of the pith. 

 Fig. 3. Vertical cut of an old stalk of the same plant. 



A. Node. 



B. Upper internode. 



C. Lower internode. 



a. Derm. 



b. Reticulated mesophloeum. 



c. Ligneous system, very much developed. 



d. Nodal diaphragm. 



e. Medullary discs. 

 /. Medullary cavities. 

 g. Roots of the discs. 



Fig. 4. Young pith very much enlarged. 



a. Vessels of the medullary sheath. 



b. Vertical cells with fecule. 



c. Shorter feculiferous cells. 



d. Prismatic cells with fecule. 

 c' — d'. Fecule. 



e. Cells where the fecule disappears. 

 /. Crystals. 



g. Nucleus. 



i. Septa of very minute cells. 

 Ic. Cells of the discs. 

 I. Angle of the cavity. 

 m. Cavity. 

 Fig. 5. Old disc cut. 



a. Dry cells folded. 



c. Rare globules. 



d. Folds. 

 e,f. Crystals. 



