VARIATIONS IN THE SPECIES. 



479 



to the depth of two and a half inches. When the diameter was less than 

 five inches, the thermometer was introduced as far as the centre of the 

 tree." 



Of the tables given by Professor Paine I select the following : 

 " Range of thermometer in the shade during the observations, which 

 lasted six hours, from 38 to 52 : near freezing at sunrise. 



"A dead upright dry tree was selected as a standard of comparison. 

 Its diameter was twelve inches. The temperature of this tree, at the 

 close of our observations, was 45 at the centre and in all other parts. 



The 'heat which is thus liberated by plants stands in the stead of a 

 certain amount of atmospheric heat, and therefore complicates the preced- 

 ing considerations. 



By such facts as those which have now been presented, we may be 

 satisfied that the well-being of plants is affected, and even Accomplish- 

 their existence determined by the influence of external agents, "onsinthe sp&. 

 and that, in this manner, they are capable of having changes cies of plants, 

 impressed upon them even in an artificial way. If we furnish to them 

 those materials or conditions which their circumstances require, they will 

 grow with luxuriance, or under an opposite state of things will dwarf 

 away ; and where, for a long period of time, such conditions are imposed 

 upon successive generations of them, a permanent change may be effect- 

 ed, those which have appeared as varieties assuming the more definite 

 form and persistency of sub-species. The general impression alluded to 

 in the last chapter, that such peculiarities are only to be extended by 

 budding or other equivalent operations, and that those which we regard 

 as different individuals are truly fragments or parts of the same individ- 

 ual, does not here properly apply. A like propagation of peculiarity is, 



