216 CHEMICAL ACTION OF 



all the agents above mentioned during its stay 

 in the cellular substance of the leaf, and re- 

 turned from thence impregnated with them 

 into the bark, may prove the source of increase, 

 and of peculiar secretions, in the vegetable 

 frame. That portion of sap sent to the tlower 

 and fruit undergoes no less remarkable 

 changes, for purposes to which those curious 

 or^^-ans are devoted ; nor is it returned from 

 thence, as from the leaves, to answer any 

 further end. The existence of those organs 

 is still more temporary, and more absolutely 

 limited to their own purposes, than even that 

 of the leaves, from whose secretions theirs 

 are very distinct. 



But when wo attempt to consider how the 

 particular secretions of different species and 

 tribes of plants are formed ; how the same 

 soil, the same atmosphere, should in a leaf 

 of the vine or sorrel produce a wholesome 

 acid, and in that of a spurge or manchineel a 

 most virulent poison ; how sweet and nutri- 

 tious herbage should grow among the acrid 

 crowfoot and aconite, we find ourselves to- 

 tally unable to comprehend the existence of 

 such wonderful powers in so small and seem- 



