338 Vegetable Physiology. 



bark and wood of the dead stem. These fibres have reached 

 the ground, supplied nutriment to the expanding bud, which 

 has at length formed a perfect tree, enclosing the original dead 



stem. 



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, or rather spines. That spines are really produced from 

 the leaf-buds may be easily ascertained by examining a grow- 

 ing shoot of the common Barberry, when their different states 

 of developement will be observed. 



The influence of light in producing the green color of leaves, 

 is remarkably shown when the buds are unfolding. The 

 stronger the sunshine, the sooner will they assume their charac- 

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

 will remain for days together almost of the same color as be- 

 fore they expanded. If during a continuance of rainy wea- 

 ther, the buds of a forest expand, their hue remains pale until 

 the sun appears, when within a few hours they assume their 

 full green color. One writer mentions a forest in this country, 

 on which the sun had not shone for twenty days. " The 

 leaves during this period were expanded to their full size, but 

 were almost white. One forenoon the sun began to shine is 

 full brightness ; the color of the forest absolutely changed «o 

 fast that we could perceive its progress. By the middle of the 

 afternoon, the whole of this extensive forest, many miles in 

 length, presented its usual summer dress." 



