318 PROTECTIVE ARRANGEMENTS OX THE EPIDERMIS. 



plantains, papilionaceous plants, and plants of the Spurge-laurel family— just those 

 plants which constitute the main part of the vegetation on the shores of the 

 Mediterranean Sea, and which possess a thickly-woven covering of hair. Indeed 

 representatives of families such as the Grasses, whose members are usually bare, 

 here appear to be quite shaggy with hair. It is also very interesting to see that so 

 many species, which have a wide range of distribution, and which, from Scandinavia 

 to the coasts of the Mediterranean, have bare foliage, can in the South protect them- 

 selves from drying up, by developing hairs on their epidermis. For instance, from 

 Northern and Central Europe as far as the Alps, the epidermis of the stems and 

 foliage of Sileue inrtata, Camjm mda Speculum, Galium rotumlifoHum, and Mentha 

 Pulegiumis smooth and bare; in the South, — particularly in Calabria, — the leaves 

 and stems of these species are covered with thick down. 



Next to the Mediterranean flora, the neighbouring Egyptian and Arabian desert 

 regions, the elevated steppes of Persia and Kurdistan, as well as the lowlands of 

 Southern Russia and the plains of Hungary, show a comparatively large number of 

 species whose leaves are thickly coated with hairs on both surfaces. Their number 

 is less than that of the flora of the Mediterranean district, because in the steppes 

 and deserts the dryness of the summer is greater than in that region, and even 

 thick hairy coverings are not alwaj r s a sufficient protection against this dryness, and 

 also because in some of these districts the dry period passes directly into a severe 

 winter, and the hairs would offer but a poor protection against the cold. Since on 

 the coasts of the Mediterranean Sea the winter temperature never falls below 

 freezing point, evergreen and grey leaves remain there unmolested, and recommence 

 their activity at the beginning of the next season. 



The successive developments of certain plant forms are very instructive with 

 regard to the relations existing between whole floral regions and transpiration. In 

 the steppes, Mediterranean district, and at the Cape, bulbous plants and annuals 

 first make their appearance; then follow the perennial grasses and woody plants; 

 and finally succulent plants and thickly-haired immortelles. The numerous tulips, 

 narcissi, crocuses, stars of Bethlehem, asphodels, amaryllises, and all the other 

 bulbous growths, which begin to sprout immediately after the first winter or sprino- 

 rain, always have bare foliage. Their transpiration is very active in consequence of 

 the rapidly-increasing temperature of the air, but the saturated soil provides a 

 sufficient substitute for the evaporating water, and also has ready in a free state the 

 food-salts which are required for rapid growth. The shrubs which sprout at the 

 same time, the peonies and hellebores, as well as the host of annuals which spring 

 up, blossom, and fructify in an inconceivably short time, almost all possess bare 

 foliage, especially in the steppes. Towards midsummer, when the drought com- 

 mences, all these plants are already in fruit; their foliage, which until now has been 

 actively at work, begins to turn yellow ami to dry up; their succulent tubers and 

 bulbs are imbedded below the surface in soil which is now as hard as a stone; and 

 the seeds which have fallen from the animal plants are easily able to survive the 

 aridity of the summer and the severity of the winter, since they are inclosed in 



