MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 379 



elongated cells, but are more commonly made up of a linear series, 

 attached end to end, as in Fig. 240. Sometimes these hairs hear little 

 glandular bodies at their extremities, by the secretion of which a peculiar 

 viscidity is given to the surface of the leaf, as in the Sundew (Drosera); 

 in other instances, the hair has a glandular body at its base, with whose 

 secretion it is moistened, so that when this secretion is of an irritating 

 quality, as in the Nettle, it constitutes 



a ' sting. ' A great variety of such FIG. 272. 



organs may be found, by a microsco- 

 pic examination of the surface of the 

 leaves of plants having any kind of 

 superficial investment to the epiderm. 

 Many connecting links present them- 

 selves between hairs and scales, such 

 as the stellate hairs of the Deutzia 

 scabra, which a good deal resemble 

 these within the air-chambers of the 

 Yellow Waterlily (Fig. 238). 



380. The Epidermis in many portion of Vertical Section of leaf of j?o- 

 plants, especially those belonging to f e ^ s ^ 



the GraSS tribe, has its Cell-Walls im- of the outer layer; c, one of the stomata; d\ 



nrpo-rmfprl with ///"/ likp tVmt nf tliP d cells of the parenchyma; L, cavity be- 



SU6X, like 9 tween the parenchymatous cells, into which 



JEquisetum (^ 345); so that when the the stoma opens, 

 organic matter seems to have been 



got rid-of by heat or by acids, the forms of the cuticle-cells, hairs, sto- 

 mata, etc., are still marked-out in silex, and (unless the dissipation of 

 the organic matter has been most perfectly accomplished) are most beau- 

 tifully displayed by Polarized light. Such silicified epiderms are found 

 in the husks of the grains yielded by these plants: and there is none in 

 which a larger proportion of mineral matter exists, than that of Rice, 

 Tvhich contains some curious elongated cells with toothed margins. The 

 hairs with which the palece (chaff-scales) of most Grasses are furnished, 

 are strengthened by the like siliceous deposit; and in the Festuca praten- 

 sis, one of the common meadow-grasses, the paleas are also beset with 

 longitudinal rows of littls cup-like bodies formed of silica. The epiderm 

 and scaly hairs of Deutzia scabra also contain a large quantity of silex; 

 and are remarkably beautiful objects for the Polariscope. 



381. Externally to the epidermis there usually exists a very delicate 

 transparent ' cuticle,' showing no decided traces of organization, though 

 occasionally somewhat granular in appearance, and marked by lines that 

 seem to be impressions of the junctions of the cells with which it was in 

 contact. When detached by maceration, it not only comes off from the 

 surface of the epiderm, but also from that of the hairs, etc., which this 

 may bear. This membrane is obviously formed by the agency of the 

 epidermic cells; and it seems to consist of the external layers of their 

 thickened cellulose walls, which have coalesced with each other, and have 

 separated themselves from the subjacent layers. 



382. In nearly all plants which possess a distinct epidermis, this is 

 perforated by the minute openings termed stomata (Figs. 270-272, c, c); 

 which are bordered by cells of a peculiar form, distinct from those of the 

 epidermis, and more resembling in character those of the tissue beneath. 

 These boundary-cells are usually somewhat kidney-shaped, and lie in 

 pairs (Fig. 273, b, b), with an oval opening between them; but by an al- 

 teration in their form, the opening may be contracted or nearly closed. 



