154 On the Freezing of Water in leacten Pipe*. 



temperature and in a less divided state than that which i.» 

 attracted from great depths under ground; hence containing 

 less combined heat, and being also, in the case of showers, 

 applied to i he earth and roots already in its fluid state. In 

 the cold seasons of winter the same cause will prevail in a 

 yet greater degree ; for, the colder the upper stratum of 

 mould, the more copious must be the ensuing condensation. 

 Thus, in proportion as the state of the ambient atmosphere 

 is more or less favourable to the vegetable process as carried 

 on by all the parts of the plant above ground; so, the greater 

 the obstacles here presented to the procedure of the same, 

 the more do they require of stimuli around their radical fibres 

 to obviate the opposing circumstances in the atmosphere, 

 These will be in some measure compensated by the addi- 

 tional stimulus of heat now imparted around the roots by 

 the vaporous condensation alluded to : yet, if the same un^ 

 favourable season be of too long continuance, this under- 

 ground stimulus will, like all other excessive stimuli, be 

 followed by an equal degree of depression on the part of the 

 individual plant so circumstanced ; and in this view a hot 

 and dry summer, by excessive exhaustion of the vegetable 

 powers from root to leaf, must prove more deleterious to 

 vegetation than a cold winter. 



From the above premises I beg to draw a conclusion, 

 consistent with the established laws of caloric, not less war- 

 rantable from actual fact than from analogy in another king- 

 dom, and conformable to the ever-prominent uniformity 

 observable throughout the various operations of nature, that 

 plants are endowed with the property of indirectly gene- 

 rating in the vicinity of their roots, by their exhaustion of 

 moisture, and consequent ascentand condensation of aqueous 

 vapour from beneath, that temperature, whichj acting as 

 a stimulus, and, hence enabling them to counteract exter- 

 nally opposing circumstances, proves most favourable to, 

 and the natural consequence of, their vegetation,-— in the 

 same manner as the effect of existence is the engendering 

 of that degree of heat within the animal system which not 

 only favours the continued performance of the various func- 

 tions of the body, but which increases as the external me- 

 dium is more cold and unfavourable to the living process, 

 and without which animal life itself would soon terminate. 

 in insensibility, torpitude, and death. 



Ki-riP'ivron. 

 May j 8, 1804. 



XXVIIL Be* 



