(Meo * A oa rst F — % 4 t ay “44 he ~. e un isi: een 
Be La “Structural pnd d Phosiolasieal Botany. 
~ 
anne el longitudinal, and transverse striations eg. 4s 
| 26, p. 18); and this s¢réatzon is also, as a tule, voy the result : ae 
Fic.,19.—Transverse section of a 
cell of the pith of Clematis vi- 
talba; p primary cell-wall; ¢ Fic. 20.—Bast-cell from the stem of Urania 
innermost thickening-layer; P guyanensis, with several shells (1, 2, 3, £) 
pore-canal ; z intercellular and simple pore-canals P; fs primary cell- . 
space. (x =80.) wall of an adjacent cell. ( x 780.) 
of an unequal absorption of water. The formation of shells, — 
in which the cell-wall is split up into two or more strata of 
Fic. 2t.—Lorgitudinal section through several cells of the epidermis of the Mis- «|; a ae 
tletoe thickened on one side only ; s thickening-layers ; c cuticle. (x 660.) 
different chemical and physical properties, must be clearly 
distinguished from the thickening layers. Each of these 
