EPIDERMIS. 



Z7 



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 Commelinaceae (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 outgrowihs 

 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 '^, Cycadeae (Kraus. /. c), Monocotyledons, as Aloe ^ 

 Agave*, Dasylirion, Hechtia^, Iris", Allium, Orchidaceae, &c., and Dicotyledons, as 



^^pm=s^^ 



Fig. 12. — Pholidophyllum zonatum, adult leaf, under surface. --/ 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 the lateral subsidiary 

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



Ficus elastica^ australis, Proteaceai ^ Nelumbium^, 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 ihe epidermis, e. g. leaves of 

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

 12-16), Nerium Oleander, many Proteaceaj '^ Helleborus foetidus", Rhinanthus, 

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



* Rauter, Entw. d. Spaltoffn. von Aneimia, u. Niphobolus. Mittheil. d. natur. Vereins f. Sleier- 

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



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



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



* Moldenhawer, Beitr. p. 103. — Oudemans, 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. Spaltoff. d. Proteaceen, N. Act, Acad. Leopold. XVI. II, and Verm. Schrift, 

 p. 245, Taf. VII. VIII. 



^ Schleiden, Grundziige, 3 Aufl. i. p. 278. 



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



'* Von Mohl, Spaltoffn. d. Proteaceen, I.e. '^ Yq„ Mohl, I.e. figs. 20, 21. 



