EPIDERMIS. 



35 



variously inclined to the slit, or bluntly angular; it has usually at the united ends of 

 the cell a different form, and also larger diameter than at the part bordering on the 

 slit. Examples, Persoonia myrtilloides and other Proteacege^ Cycas^, Psilotum, 

 Equisetum, Coniferse, Restiaceae, Grasses, Calycanthus ^, Scirpus, Iris, &c. Along 

 the slit, but at some distance from it, run in most cases on each guard-cell two 

 ridge-like protuberances (belonging to the membrane, see Sect. 14), one on the outer, 

 the other on the inner surface, the corresponding ones being continuously 

 connected at the ends of the slit. The ridges are channelled and concave on 

 the side facing the slit, and convex on the other side, at the free edge they 

 are sharp, and thus appear in the transverse section in the form of sharp teeth. 

 The outer aperture, the entrance (Eingang), and the inner, the exit (Ausgang) of the 

 slit are thus bordered by the sharp edges of the ridges ; through the edge of the 

 entrance one enters into the /rotit cavity (Vorhof), which widens out between the 

 channelled faces; through the edge of the exit into the similarly formed but usually 

 much smaller back cavity (Hinterhof) ; the pore-passage (Spaltendurchgang *), which 



Fig. 10. — Hyacinthus orientalis, leaf, cross section, e — e 

 epidermal cells ; s entrance of the stoma, which lias been 

 cut through transversely in the middle ; ;' respiratory 

 cavity between the parenchymatous cells,/. (800). From 

 Sachs' Textbook. 



Fig. II. — Cross section through the leaf of 

 Pinus Pinaster, j guard-cells ; / passage of the 

 stoma; v the furrow, limited internally by the 

 stoma; c cuticular layers; a limiting lamellae be- 

 tween the epidermal and the hypodermal scle- 

 renchymatous cells ; g^ chlorophyll-parenchyma 

 (800). From Sachs' Textbook. 



widens towards both cavities, leads between the parts of the section of the guard- 

 cells which are broadest, and nearest to one another, from the front to the back 

 cavity. The ridges of exit and of entry are extremely various in form and size, 

 (comp. Sect. 14), they are not uncommonly very small, especially the ridge of exit, 

 and therefore easily overlooked. It is rare for both or for the ridge of exit to 

 be really absent. The latter alone is absent in Elymus arenarius, Bromelia Caratas, 

 Ilakea saligna, ceratophylla, Banksia sp.; both in most observed Coniferse^ (Fig. 11), 

 Cycadese", Ephedra, Psilotum, Azolla''. 



' Mohl, Verm. Schr. p. 248. ^ Kiaus, t.c. p. 320. ^ Pfitzer, I.e. 



* 'Eigentliche Spaltoffnung,' Von Mohl, Bot. Zeitg. 1856, p. 697, Taf. XIII. Here the subject 

 is explained. Many good drawings by Strasburger in his Beitrage z. Entvvickelungsgeschichte d. 

 Spaltoffnungen, Pringsh. Jahrb. V. p. 297, Taf. 35-42. 



^ Hildebrand, Bot. Zeitg. i860, Taf. IV. — Strasburger, loc. cit. fig. 145. 



^ Kraus, I.e. — Strasburger, fig. 143. ' Strasburger, Ueber Azolla, Taf. III. 



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