PROTECTIVE ARRANGEMENTS ON THE EPIDERMIS. 317 



the Sierra Nevada, and the mountains of Greece are unusually rich in such 

 forms. 



If plants growing in such situations are protected against the dangers of too rapid 

 and too abundant evaporation, how much more must this be the case in those regions 

 where, with the increasing warmth of summer, the number of showers steadily 

 diminishes; and where the soil becomes dried more and more deeply, so that all the 

 plants whose roots are near the surface are unable to derive a drop more water from 

 it ? All plants which are to survive the dry period in such places must during this 

 time entirely cease transpiring — they must, as it were, turn into a chrysalis and 

 sleep during the summer. They actually do this in all sorts of different ways, and 

 by tlie most diverse means. One of the commonest and most widely spread 

 methods is, without doubt, by having the transpiring organs clothed with a thick 

 covering of dry air-containing hairs. Plenty of examples of this are furnished 

 by the flora of the Cape, Australia, Mexico, the savannahs and prairies of the New 

 World, and the steppes and deserts of the Old. In the dry elevated plains of 

 Brazil, Quito, and Mexico, there are large tracts covered with gregarious spurge- 

 like growths and grey-haired species of Croton, and when the wind blows, moving 

 these bushes to and fro, undulations are set up over wide extents of country, the 

 whole appearing like a billowy sea of grey foliage. A similar picture is presented 

 by the Painciras belonging to the Compositse, or by the Lychnophora, on the high 

 plains of Minas Geraes in Brazil. Nowhere in the whole world, however, does the 

 presence of hairs on foliage, as a protection against exhalation, appear in such an 

 abundant and varied manner as in the floral region surrounding the Mediterranean, 

 known as the Mediterranean district. The trees have foliage with grey hairs; the 

 low undergrowth of sage and various other bushes and semi-shrubs (for which the 

 name " Phrygian undergrowth ", used by Theophrastus, may be retained), as well as 

 the perennial shrubs and herbs growing on sunny hills and mountain slopes, are 

 grey or white, and the preponderance of plants coloured thus to restrict evapora- 

 tion has a noticeable influence on the character of the landscape. He who has only 

 heard from books of the evergreen plants of the Greek, Spanish, and Italian floras, 

 feels at the first sight of this grey vegetation that he has been in some degree 

 deceived, and is tempted to alter the expression "evergreen" into "ever grey". Every 

 conceivable sort of hair structure is to be met with in these parts — coarse felt-work, 

 thick velvet, and white wool mixed in endless variety. Here is a leaf looking as if 

 covered with a cobweb; there another as if bestrewn with ashes or clay; here a leaf 

 surface, covered with closely pressed hairs or scutiform scales, glistens like a piece of 

 satin; and here again is a plant with such a long flock of hair that one might 

 imagine that sheep in passing had left pieces of their fleece hanging on it. There is 

 hardly a family in the flora of the Mediterranean district which does not possess 

 members richly provided in this way. The Composites are the most remarkable in 

 this respect, especially the genera Andryala, Artemisia, Evax, Filago, Inula, and 

 Santolina; then come the Labiates of the genera Phlomis, Salvia, TeucHum, 

 Marrubium, Stachys, Sideritis, and Lavandula; rock-roses, bindweeds, scabious. 



