R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 295 



Bast Parenchyma. — This sometimes alternates with the bast 

 vessels, forming broader or narrower tangential bands, but some- 

 times it is scattered more irregularly between them, and agrees 

 with wood parenchyma in structure ; its walls, however, are less 

 strongly thickened, and these thickening layers usually remain 

 unlignified. The contents during the resting period are starch, 

 which becomes dissolved at the commencement of renewed growth, 

 and in the old bast parenchyma of ligneous plants, crystals of 

 oxalate of lime are also seen. 



Bast Vessels. — Lattice-cells or cribrose tubes are found sometimes 

 scattered irregularly through the bast parenchyma, singly or in 

 groups {Clematis, Acer, Fagus), sometimes arranged in tangential 

 bands of one or more rows, often including single parenchym cells 

 {Bi'gnonia, Tilia, Vitis,&c.). The laticiferous bast vessels may be 

 scattered within the bast-fibre groups, or occur at their outer 

 border, or pass even into the cortical tissue (Ficus, Neriiwi, &c.), 

 and in Carica they stand between the vessels of the wood part, as 

 well as in the bast part and the bark. 



Intermediate Tissue or Medullary Rays. — This appears either 

 between- the primitive Vascular bundles, in few or many rowed 

 series of cells, running in a radial direction, or within them, in 

 one or few rows. In the former case it proceeds immediately from 

 the tissue of the thickening ring which separates the cambial 

 bundles from each other, and reaches from the pith to the rind, 

 and thus keeps divided the primitive Vascular bundle. These 

 are named Pith rays or Pith-hark rays. In the latter it 

 takes its origin immediately from the cambium of the Vas- 

 cular bundle by division of the cambial mother cell, and we 

 may distinguish it into Primary bundle rays, which arise in the 

 primitive bundle, and Secondary bundle rays, which first appear in 

 the later formed wood and bast. By the bundle rays the wood and 

 bast parts become cleft into smaller wedge-shaped bundles pro- 

 jecting more or less deeply into the substance, but always most 

 distinctly seen in the wood. 



The Pith-rays and Bundle-rays of woody Dicotyledons consist 

 of parenchym cells greatly elongated in a radial direction, but 

 with the other diameters much shortened, so that in longitudinal 

 section they form a muriform tissue ; at the ends, however, next 

 the pith and the bark, the cells are more equal in diameter, because 

 they proceed from the primitive dividing tissue of the cambial 

 bundle. The thickening of the cellulose case is faint in the bast 



