LECT. VII.] ANATOMY OF STKMS. 323 



depends on the exposure of its juices to the light 

 and on the resinous nature of these juices. He re- 

 gards the whole of the cellular integument, also, 

 as a glandular body serving to separate the trans- 

 pirable matter from the other fluids * ; an opinion 

 which I shall have occasion to notice more par- 

 ticularly when we investigate the functions of 

 the stem. The cells of the interior portion, in 

 the young shoot of the Horse Chesnut, are very 

 regular hexagons, except in those places where 

 there is any pressure, or where the adjoining 

 parts require a variation of form, when a change 

 takes place; but, independent of these circum- 

 stances, the pure hexagonal form does not prevail 

 in the stems of every species of the natural tribe 

 of plants under examination. Thus in Privet, 

 Ligustrum vulgare, the cells are variously formed, 

 some being nearly circular, others rudely ellip- 

 tical, and some very obscurely heptagonal : in the 

 Elder, Sambucus nigra, they are equally irregu- 

 lar ; in the Common Lilac, Syringa vulgaris, the 

 proportion of real cellular matter compared with 

 that of the semi-organized pulp is small, and the 

 cells, which are of an oblong figure, are com- 

 pletely filled with minute amylaceous granules ; 

 and this is the case, also, in the Laburnum, 

 Cytisus Laburnum, in which, however, they 



* Elemens de Physiologic vegetate, l ere par tie, p. 103. 



Y-2 



