. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. MAINTENANCE OF A FREE PASSAGE FOR AQUEOUS VAPOUR. 303 it with all other rolled leaves, whether they belong to Cape plants or to heath plants of the Baltic lowlands. It cannot be doubted that the mechanism of rolled leaves, as just described, furnishes a protection for the stomata against moisture, and keeps open a passage for aqueous vapour and excreted gases. The question is now only how it comes about that this arrangement is to be met with in plants of such widely distant countries and under such
. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. MAINTENANCE OF A FREE PASSAGE FOR AQUEOUS VAPOUR. 303 it with all other rolled leaves, whether they belong to Cape plants or to heath plants of the Baltic lowlands. It cannot be doubted that the mechanism of rolled leaves, as just described, furnishes a protection for the stomata against moisture, and keeps open a passage for aqueous vapour and excreted gases. The question is now only how it comes about that this arrangement is to be met with in plants of such widely distant countries and under such differences of climate? In order to understand this clearly, let us imagine ourselves in some of the regions which are specially characterized by the abundance of plants with rolled leaves. First, on one of the high ridges of the Central Alps, where the low-lying Azalea spreads a thick covering over the soil, where Erica carnea in great quantity. Fig. 72. —Vertical Section through a Rolled Leaf of the Trailing Azalea (.Azalea protsumbens); x 140. covers broad slopes, where Bryas octopetala, Salix reticulata, Homogyne discolor, Saxifraga coesia, and many other plants which possess evergreen rolled leaves weave their carpet over the stony earth. The ground in which all these plants are rooted, and from which they draw their fluid nourishment, has many natural dikes and retains a large quantity of water, not only from the melting of the heavy winter mantle of snow, but also from the abundant rain of summer. For weeks together the heights are wrapped in a cold mist which saturates everything with moisture, and drops of water hang from the stems and leaves, unable to evaporate as long as the air remains so supercharged with vapour. At length the sky clears again, and the water on the plants begins to disappear. But even during the fine night following, all the plants become covered with a very heavy dew in consequence of their rapid cooling and radiation, and this not unfrequently
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
