The Vegetative Anatomy of Molinia cserulea. 67 
by an exceedingly strong band of very thick walled elements (Pig. 7) 
and the woody tissues, composed of annular tracheides and pitted 
vessels, are both abundant and strongly thickened. Each bundle 
is accompanied by a pair of longitudinal rows of peculiar cells on 
both surfaces of the leaf (P), marked off in transverse section by 
having a darker colour and a concave instead of convex outer wall. 
Examination of a piece of stripped epidermis shows these to be 
provided with dumb-bell shaped plates (Fig. 9, A), probably siliceous 
whence they may be called plate-cells, and the function of these 
cells may be excretory. It will be gathered from these details that 
the Molinia leaf is exceedingly rich in wood elements and stereome 
and this is the explanation of the rigidity of the leaves. As Lewton 
Brain remarks, “ the leaf is peculiar in the great strength and 
abundance of its mechanical tissue,” a remark which would also 
apply to the plant as a whole. 
Fig. 8. A. Motor mechanism of leaf, transverse section. B. Teeth by 
motor cells. Lettering :— a., assimilating tissue ; b., “ basal ” cell ; s., stoma ; 
tooth. A x 500, B x 800. 
The motor mechanism (Fig. 8) is strongly developed and, after 
the bundles, constitutes the most conspicuous feature in the 
