216 R. BRAITIIWAITE ON THE HISTOLOGY OF PLANTS. 



changes the whole cellulose ; the primary is most changed, but the 

 tertiary is often not altered. 



Suberification appears only in the layers of the plant-tissue 

 exposed to atmospheric influence. In the epidermis it occurs 

 mostly in the outermost cuticular layers, lying under the true 

 cuticle ; but here also the whole cellulose is not transformed. The 

 young cork cells also, after treatment with caustic potass, give an 

 indication of cellulose, but in the older layers it entirely disappears. 



Intercellular Substance and Cuticle. — These may be mentioned 

 here, as they seem to be identical in constitution, and both altered 

 conditions of cellulose. They may be regarded as the first coat 

 separated from the primordial membrane, within which the true 

 cellulose layers are deposited. 



Illustrative Figures. 



Plate 8. 



1. — Stellate cell from wall of air passages in Butomus umhellatus. 

 X 360. 



2. — Milk vessel from Carica microcarpa. X 400. 



8. — Unilaterally thickened cells from cuticle of a branch of 

 Mistletoe. X 660. c. cuticle ; p. primary ; s. secondary ; 

 t. tertiary layers. 



4. — Cell thickened in the angles from leaf of a Jungermania. 

 X 660. 



5. — Section of a concentrically thickened bast cell from Larch, 

 showing three pore canals. X 780. 



6.— Section of a wood cell of Beech, the secondary deposit not 

 laminated. X 780. 



7. — Ringed cell from capsule wall of Pellia epiphylla. X 400. 



8. — Cell with double spiral band from anther-wall of Pumpkin, 

 X 400. 



9. — Striation of the cellulose case. Fragment of an abnormally 

 thickened wood-cell from inner part of the annual ring of a 

 branch oi Pinus silvestris, with spiral bands of inner, secon- 

 dary, and tertiary layers. At x only the lower wall of the 

 cut cell is seen. X 900. 

 10. — Parenchym cell from partition of Walnut. X 660. 



