324 PROTECTIVE ARRANGEMENTS ON THE EPIDERMIS. 



joined to one another, a star-shaped, ribbed, multicellular plate, indented at the 

 margin, is produced (see %. 78 6 ). These plates are generally flat, lie level on 

 the surface of the leaf or stem, overlap one another with their indented margins, 

 and cover the green surface of the leaf so completely that it appears to be white 

 instead of green, and invest it with a bright, almost metallic, lustre. Such leaves 

 are said to be "scaly" (lepidotus). The best known examples of such leaves, 

 covered with shining silvery hair-scales, are those of Mceagnus and of the Sea 

 Buckthorns (Hippophae). If the plates are bent, irregularly fringed, and lustreless, 

 the leaf covered with them looks just as if it were strewn with bits of clay, and is 

 said to be " clayey " (furfwraceus). Examples of this are well shown by the leaf- 

 coverings of many plants allied to the Pine-apple (Bromeliacese). When the top 

 cell of the hair is supported on a moderately high pedestal, and is divided into 

 numerous radiating daughter-cells which diverge from one another, a structure is 

 produced which is somewhat like a knout, or, if the radiating cells are short, like a 

 sea-anemone (Actinia). This form of hair is seen, for example, in the Southern 

 and Eastern European Phlomis, in many mulleins (Verbascum Olympicum), and, 

 with multicellular pedicels, on the leaves of Gorrea speciosa, an Australian shrub 

 (see fig. 78 4 ). Occasionally a branched hair produces several whorls of branches 

 above one anothej-, and then hair-structures are formed which resemble stoneworts 

 (Characese) or miniature fir-trees under the microscope. When many such tiny 

 tree-like hairs are placed close together with interwoven branches, they look under 

 a magnifying-glass like a small plantation, and the analogy is heightened if one- 

 storied tree-shaped hairs, like the undergrowth in a high forest, occur under the 

 higher many-storied ones. This is the case in the Torchweed, Verbascum thapsi- 

 forme, whose hairs are represented in fig. 78 * . Hair-structures like these appear 

 to the naked eye like flock, and are described as " floccose " hairs (pili floccosi). 

 Many of these have the peculiar habit of rolling themselves together into small 

 balls, which make the leaf-surface look as if it were bestrewn with coarse white 

 powder. This is the case, for example, in the mullein known as Verbascum veru- 

 lentwm. 



In the crowded condition of stellate and tufted hairs, of branched floccose and 

 unbranched woolly hairs, it is unavoidable that the neighbouring hair-cells should 

 cross one another, intertwine, and be more or less interwoven; and thus arises a 

 felted mass which covers the surface of the organ in question. Such hair-masses 

 are termed " felt " (tomentum), and the varieties are distinguished as " felted " (or 

 " tomentose ") stellate or woolly hairs, &c. Often the felt only forms a thin loose 

 layer, through which the green of the leaf -surf ace can be seen; but occasionally it 

 is so thick that the leaf appears snow-white. 



While in all these cases the covering which protects the leaves and stem of the 

 plant from over-transpiration is woven from air-containing cells, cylindrical and 

 elongated — usually, indeed, very much elongated — in some thick-leaved plants, 

 especially in species of the genus Rochea, a native of the Cape, these cells become 

 vesicular and distended; they are arranged in rank and file adjoining one 



