EPIDERMIS. 



37 



cavity situated beneath the stoma is directly bounded by the lateral walls of the 

 neighbouring epidermal cells, e.g. the leaves of Orchis latifolia (Von Mohl, /. c), the 

 very large-celled epidermis of the leaf of the Comraelinacese (Strasburger, /. c. Fig. 

 150), Claytonia perfoliata (1. c. Fig. 120), and many others. 



More commonly where the height is unequal, the guard-cells lie so that their 

 inner walls fall approximately in the same plane as those of the epidermal cells 

 (comp. Figs. II, 18, &c.). They form then the bottom of a depression, through 

 which one approaches the stoma from without. This is surrounded by the neighbour- 

 ing epidermal cells, and is often over-arched at its outer margin by outgrowths 

 of these, so that the mouth is considerably reduced. This is the case in the majority 

 of tough-skinned leaves and green stems ; leaf of Polypodium lingua ^ Equiseta 

 cryptopora (comp. our Fig. 23, Sanio, Linnaea 29, 385, Taf. III. Milde, Mono- 

 graphia Equisetor.), Coniferse '■', Cycadese (Kraus. /. c), Monocotyledons, as Aloe ", 

 Agave \ Dasylirion, Hechtia ^ Iris », Allium, Orchidaceee, &c., and Dicotyledons, as 



Fig. 12.— Pholidopliyllura zonatum, adult leaf, under surface. A superficial view of a piece of Epidermis with a stoma and its 

 subsidiary cells. B median transverse section through a stoma ; the guard-cells are pushed outwards by tlie lateral subsidiary 

 cells, which have been pushed down beneath them (390). 



Ficus elastica '', australis, Proteaceaj ', Nelunibium ", Dianthus Caryophyllus, and 

 many others. 



Independently of this relation of height the case occurs that the surrounding 

 epidermal cells are so pressed against the stoma that the latter rises a greater or less 

 distance into the air above the outer surface of the epidermis, e. g. leaves of 

 Chrysodium vulgare ", Aneimia Phyllitidis, hirta ", Pholidophyllum zonatum (Figs. 

 1 2-1 6), Nerium Oleander, many Proteacese '^ Helleborus fcetidus", Rhinanthus, 

 species of Primula, many Labiatse, Pyrethrum inodorum, &c. 



' Rauter, Entw. d. .Spaltoffn. von Aneimia, u. Niphobolus. Mittheil. d. natur. Vereins f. Steier- 

 mark. Bd. II. Heft 2 (1870). 



" Hildebrand, Bot. Zeit. i860, Taf. IV. 



' Schacht. Lehrb. Taf. III. p. 24. — Strasburger, I.e. figs. 114, 115. 



' Moldenhawer, Beitr. p. 103. — ^Oudetaans, Comptes rendus, Acad. roy. Amsterdam, vol. XIV 

 (1862). 



' Schacht. I.e. Taf. IV. pp. 9, 12. — Unger, Anat. u. Phys. p. 192. 



^ Unger, I.e. p. 191.— Mohl, Verm. Schr. Taf. VIII. 



' Strasburger, /. e. fig. 133. 



' Von Mohl, Ueber d. Spaltofi". d. Proteaceen, N. Act, Acad. Leopold. XVI. II, and Verm. Schrift. 

 p. 245, Taf. VII. VIII. 



° Schleiden, Grundzuge, 3 Aufl. i. p. 278. 



" Strasburger, I.e. figs. 47, 48. " I.e. figs. 50, 57. 



" Von Mohl, Spaltoffn, d. Proteaceen, I.e. '^ Von Mohl, I.e. figs. 20, 21. 



