GROWTH OP PLANTS IN ATR. 123 



1 74. In one of the hot-houses in the Botanic Garden of Edin- 

 burgh, a plant of the Ficus Australis (the Fig of New Holland) 

 was caused to grow entirely without earth, by gradually with- 

 drawing from the pots the several roots contained in them. The 

 plant was well watered twice a day, and put out roots freely from 

 all parts of the stem and branches, by which it appeared to gain 

 an ample supply of nourishment ; for it produced a very full crop 

 of fruit, in the autumn after the earth was removed from the last 

 set of roots. Even when a plant attaches itself by roots to the 

 soil or rock, these may serve only for its support, and may not 

 contribute anything to its growth. 



175. Many succulent Plants of warm climates exist in this 

 manner ; clinging to the faces of the barest cliffs, or rising out of 

 the most dry and barren sand ; deriving their supplies of moisture 

 and other aliment, therefore, entirely from the atmosphere. It is 

 interesting to remark, that most of these plants contain in their 

 juices the substance caoutchouc (commonly known as Indian- 

 rubber) and also wax ; and the moisture obtained from the atmo- 

 sphere is prevented from evaporating (which even the thick cuticle 

 would not prevent it from doing, under the influence of a burn- 

 ing sun), by a thin layer formed by the drying of these juices 

 around them ; which, like a waterproof cloak, keeps in the 

 vappur that would otherwise be raised, so that the tissue of these 

 plants becomes turgid with their juices, although so little is 

 absorbed. 



176. But the majority of Vegetables require a larger and more 

 certain supply of their various kinds of aliment, than the atmo- 

 sphere can furnish ; and, by the prolongation of their roots into 

 the soil, they are enabled to obtain this, in a manner, however, 

 which requires some little explanation. What is commonly 

 termed soil or mould consists of two kinds of ingredients ; it is 

 partly composed of the materials of the rock beneath, the par- 

 ticles of which are gradually separated from each other, by the 

 action of the atmosphere, of water, and of the roots of growing 

 Plants, as formerly explained (. 108) ; and partly of the 

 remains of former races of Plants, which are in process of decay. 

 The former sometimes exist almost alone ; and the latter, in land 



