200 PLANT ANATOMY, 
united are also very manifold. We may thus distinguish struc- 
tures intended to protect the organs of the plant from the in- 
fluence of bending, pressure, traction, or laceration at the 
edges or margins (for instance, of leaves). 
The stone-cells (sclereids,’ compare also pages 156 and 171), 
as one of us (T.) has shown, also possess various mechanical 
functions. In seeds which do not possess a thick-walled en- 
dosperm, there is found, for example, a hard endocarp, consist- 
ing of stone-cells (Figs. 115, 87). This often consists of very 
Fic. 116.—Transverse section through a tea-leaf, with the characteristic, branched 
sclerenchyma cells. The palisade-parenchyma, which is richer in chlorophyll, is of 
a darker color. At the right of the figure are sclereids, isolated by maceration 
(Tschirch), _ 
variously adjusted rows of cells, and can therefore also endure 
strong pressure and great expansion or straining (as by germina- 
tion) without becoming ruptured. The function of the 
sclereids, which are so characteristic of tea-leaves (Fig. 116 *), is 
_ ‘The tissue of stone-cells, in accordance with Mettenius, may be 
termed sclerenchyma (see pages 156 and 172), Compare Tschirch, 
_ “ Beitrége zur Kenntniss des mechan. Gewebesystems.” Pringsheim’s— 
dele 16 
_ *In young tea-leaves, however, these astrosclereids are wanting. 
