EPIDERMIS. ^ 



If one surveys the cases in which this occurs, it will be seen that the foliage of plants 

 with delicate leaves, which live in shad}' places, is especially concerned, such as that 

 of most i'^erns, further Impatiens nolitangere, Melampyrum sylvaticum, Galeopsis 

 tetrahit, Ranunculus Ficaria, Epilobium roseum ; also Listera ovata, and Staphylea 

 pinnata ' may perhaps be added. On the other hand, however, the same phenomenon 

 occurs also in inhabitants of sunny places, as Mercurialis annua, Lamium purpureum, 

 Caltha palustris, to which examples many others might easily be added. Epidermal 

 cells of parts growing under water are, on the contrary, rich in chlorophyll grains 

 and the bodies included in them, richer even than any other tissue of the species. 

 Thus in the leaves ofCeratophyllum, Aldrovanda, Ranunculus aquatilis, Potamogeton, 

 Hydrilleae ^ &c. In Elodea canadensis, and its allies, the chlorophyll-containing leaf 

 consists in the main of only two layers, which originate, like scales, from the epidermis 

 of the stem. Brongniart ^ already showed that in species typically submerged, 

 but which also occur as land plants, such as Ranunculus aquatilis, the submerged 

 epidermis is rich in chlorophyll, while that of the land form is without it, and that an 

 intermediate condition occurs on transition from one habit to the other. But the 

 rule just given is not general for all water plants. Both the amphibious species of 

 Callitriches and C. autumnalis which only occurs submerged, have an epidermis 

 without chlorophyll*. 



Sect. 12. In contrast with the epidermal cells, the guard-cells of the stomata 

 are always very rich in protoplasm, chlorophyll, and the bodies included in 

 the latter, especially starch grains ; in colourless plants only the last-named bodies 

 are present. The subsidiary cells of the stoma resemble the epidermal cells as 

 regards the properties in question. No peculiar phenomena, i.e. such as do not 

 belong generally to the different cells of the plant, are known for the cell-sap of the 

 epidermal and guard-cells, and the bodies which occur dissolved and suspended in it. 

 It is true they have as yet hardly ever been carefully investigated. This assertion is 

 only confirmed by the casual statements made about oily drops suspended in cell- 

 sap, and masses or drops containing tannin in the Cycadese (Kraus), about tannin 

 generally in the Crassulaceoe, Rosa, Ficus, Camellia, the Saxifragas ^, &c. : also about 

 more or less soHtary crystals of Calcium oxalate in the leaves of Tradescantia 

 discolor. Begonia manicata, argyrostigma, and Hakea saligna, octohedral crystals in 

 Asplenium Nidus, klinorhombic crystals which completely fill the small cavity in 

 scattered or grouped cells of the leaf of Ilex paraguayensis ". 



Thomas'^ describes in the leaves of Pinus Pumilio, Pinaster, and austriaca, 

 epidermal cells whose contents are dried up, and replaced by air in consequence 

 of rupture of the membrane. It may, however, be conjectured that this description 

 refers to abnormal conditions. 



' Sanio, Botan. Zeitg. 1864, p. 196. Compare also Kraus, in Pringsheim's Jahrb p. 314. 



^ Caspary, Pringsheim's Jahrb. I. p. 348. — Botan. Zeitg. 1859, p. 125. 



^ Ann. Sci. Nat. i Ser. torn. XXI. (1830) pi. 17, figs. 3 and 6. — Further, Askenasy, Botan. Zeitg. 



1870, I.e. * Hegelmaier, Monogr. p. 9. 



' Compare Sanio, I.e.; Kraus, I.e.; Wigand, Botan. Zeitg. 1862, p. 121; Engler, Botan. Zeitg. 



1871, p. 888. 



^ Kraus, /.c. — Meyen, Physiologic, I. p. 227. — Goldmann, Botan. Zeitg. 1848, p. 557. 

 ^ Pringsheim's Jahrb. p. 26. 



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