Nature, Longevityy and Size of Trees. 19 



feebly exerted. Is it, then, an unfair inference, that the ab- 

 sence of that change, and the inability to undergo it in any 

 tissue, are tantamount to this tissue being the seat of no vital 

 action, or destitute of vitality, after its formation is com- 

 pleted l 



3. In the third place, we know, that after a time the heart- 

 wood decays and disappears, and that this change may go to 

 such an extent as to destroy a large part of the entire thick- 

 ness of the trunk, without, however, in the least impairing 

 the vegetation going on at the extremities, and on the exterior 

 of the tree. This it is easy to understand, according to the 

 view here taken of the nature and duration of life in trees ; 

 but very difficult on the supposition of an entire tree consti- 

 tuting a single or an individual plant, and being endowed 

 with vitality in its every part. On this supposition, such a 

 change occurring in the heart-wood should spread to the ad- 

 joining living tissues, and sooner or later, but before long, 

 destroy the vitality of the whole fabric. This, however, does 

 not happen ; nor is the complete and premature decay of an 

 entire tree ever to be ascribed to the agency of such a cause. 



It may be supposed, however, that although the old stems 

 and roots, after the year of their formation, are the seat of 

 no nutritive organic change, and actually decay and disappear 

 in the course of years, the circulation of the sap moving 

 through them the following and during several subsequent 

 years, is a clear proof that they retain their vitality for a 

 much longer period than is here allowed. 



It does not therefore follow, however, that the parts in 

 question are alive. To warrant such an inference, it must 

 bo shewn that they contribute actually and actively towards 

 the movement, and that, too, in a way not referable merely to 

 their porosity, or to any other simply physical property which 

 they may possess. The experiment is well known of strew- 

 ing cress or mustard seeds on a vessel covered with flannel, 

 placing that in a saucer filled and regularly supplied with 

 water, and of finding the seeds vegetating and covering the 

 vessel with living plants— the flannel, by reason of its poro- 

 sity, conveying the water upwards from the saucer to the 

 living seeds and plants. No one, however, would say that 



