DEVELOPMENT OP LEAF-BUDS.-r-THORNS. 



197 



more resembling wood, and this in the next season by another ; 

 so that this portion of the structure, like the aerial roots of the 

 Pandanus, may be^egarded in the light either of stem or roots, 

 an idea which may, perhaps, be applied to the woody stem in 

 general. 



307. Leaf-buds are always formed from the cellular portion 

 of the stem or branches, on which the function of extending the 

 growth of the individual seems especially imposed. They may 

 be distinctly traced, in young 



branches, to the pith ; and where 

 this has dried up, they may be 

 seen to arise from the medullary 

 rays. Sometimes they are stunted 

 in their growth, and instead of 

 being developed into branches, 

 they remain as thorns; which are 



. FIG. 76. ORIGIN OF BRANCHKS 



neither more nor leSS than short , branch originating in the first year, 



pointed branches, containing much direct from the P ith ' 6 - a bud OTi - 



5 ginatirig from the cellular portion of 



dense WOOdy Structure (by which the third woody layer. 



they are rendered extremely 



strong), and being destitute of leaves. Any one may satisfy 

 himself of this, by looking at the common Black-thorn, in which 

 many intermediate conditions may be seen. Now under culti- 

 vation, these undeveloped buds may be caused to become fertile 

 branches ; and this is another of the modes in which, in Lin- 

 nseus's phrase, " wild fruits" may be " tamed." (. 236.) There 

 are no thorns stronger than those of the Acacia tribe, which are 

 sometimes 5 or 6 inches long, formed with great regularity, and 

 strong in proportion. The plants which bear them are often 

 encouraged to grow in the East, for the purpose of forming 

 hedges, which serve most effectually to keep out intruders, unless 

 these are covered with some almost impenetrable envelope. 



308. The influence of light upon the green colour of the 

 leaves is remarkably shown, when the buds are unfolding. The 

 stronger the sunshine, the sooner will they assume their 

 characteristic hue ; and, on the other hand, in dark dull weather 

 they will remain for days together, almost of the same colour as 



