188 LEAVES FROM THE BOOK OF NATURE. 



that the drier and sandier the soil is on which plants grow, 

 the more deeply furrowed are their leaves. In large trees, 

 therefore, a constant stream of water flows from the end 

 of the leaf to its stem, and from branch to branch until 

 it reaches the trunk, and then in the deep furrows and 

 crevices of the bark down to the roots, so that not a 

 drop of the precious nutriment is lost. Water-plants, on 

 the contrary, needing no such ingenious contrivances, as 

 they have an abundance of the element all around them, 

 display smooth leaves, often so highly varnished that the 

 water runs off or stands in silvery pearls on the dark 

 green surface. 



All plants are greedy consumers of water, and know 

 how to obtain it, by some peculiar, as yet unknown pro- 

 cess, even in such regions of the tropics, where for half 

 the year no cloud darkens the ever-serene sky, and where 

 not even dew is given to refresh the panting vegetation. 

 Their power, in this respect, is as great as it is mys- 

 terious. The most succulent plants of the tropics cling 

 to the faces of barren cliffs, or rise from dry, dust-like 

 sand. It is true, their leaves contain both caoutchouc and 

 wax, and are covered with a thin layer of these substances, 

 as with a water-proof cloak, to prevent evaporation under 

 a burning sun. Some plants, however, support themselves 

 not only, but actually increase in weight when suspended 

 in the air, and unconnected with any soil, as the common 

 houseleak and the aloe. The so-called air-plant, perhaps 

 the most remarkable of the whole vegetable kingdom, is 

 but a single leaf, without stem or root, and yet it is able 

 to maintain life, to grow and to blossom, if only hung 



