538 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



spiration ; so its stems often acquire huge dimensions, being made of a* 

 thin-walled, succulent tissue, as seen in Cacti, Euphorbias, Stapelias, 

 &c,, with a very thick skin to arrest the loss of water. There being 

 an insufficient supply of water, the size of the leaves is reduced ; while 

 boughs often remain short and harden, often ending in spines, as in our 

 Furze. 



Not only is it a matter of induction, or the accumulation of innumer- i 

 able independent cases, where the same results follow under similar 

 conditions — as those of Mexico for Cacti and Agaves, and of Africa | ; 

 for Euphorbias and Aloes — but an abundance of experimental proof i 

 is afforded. Thus, if spiny plants are grown with plenty of water, , 

 the spines grow out into leafy branches, as in the Eest Harrow and \ 

 Furze. The fleshy plants of the seaside, as the Samphire, can be i 

 imitated by watering cress or other inland plants with salt and water, 

 and they become fleshy too. Dwarf alpine plants may become tall 

 in low altitudes, and lowland ones become dwarfs when grown high 

 up, and so on. 



In every case the non-living materials, as cellulose, necessary for 

 building up the plant, must be directed to the places required by the 

 living protoplasm. 



With regard to the question before us — Whence came this responsive | 

 power in all living beings to vary structures so as to become adapted | 

 to changed conditions of life? It resides in the protoplasm and 

 nucleus. In other words, it is a property of life; and saying that is 

 saying all we know and are likely to discover from Nature. 



It is a matter of common experience that architects and engineers 

 so far " follow Nature " knowingly or unconsciously by adopting 

 precisely the same mechanical methods as are to be found in organic t 

 beings, and for the same purposes. Thus the wood of stems con- | 

 stitutes a number of girders ; and when they unite into a tube the stem j 

 may become hollow, as is a straw; but then cross-diaphragms are j 

 inserted at the joints, just as a hollow iron pillar is provided with them i 

 where necessary for strength. Cables are made of several spirally I 

 twisted ropes; some lianes are similarly constructed. 



If man, therefore, constructs all sorts of mechanical appliances , 

 to meet the necessities of his work, so do plants and animals. These j 

 both feel strains, stresses, and weights, and consequently set to work 

 to meet and overcome them. 



All this is done under the directivity of life. 



If, then, induction be trustworthy, the abore brings us to the 

 inevitable conclusion that it is life which is the dii;i; ctoi of energy in all ^ 

 organic beings. 



