254 Dr. Daubeny on the Degree of Selection exercised by Plants, tvith regard 



with a similar intent to my own, tlie plants operated upon, in order that all 

 external sources for the supply of earthy matter might be cut off, were made 

 to vegetate either in washed sand, in sulphur, in pounded glass, in small shot, 

 or in certain metallic oxides. 



It occurred to me, however, that without placing them under circumstances 

 so unnatural, and consequently so unfavourable to growth, the same end would 

 be fulfilled if the seeds were sown in some earth which, though foreign to 

 their constitution, agreed, nevertheless, more nearly in mechanical properties 

 with those contained in the soils in which they were wont to grow. 



It was with this intent that I was originally led to select as a soil for my 

 plants the sulphate of strontian, which is obtained in abundance near Bristol, 

 reduced to fine powder : and having found that the ashes of plants which had 

 been reared in this matrix seemed to contain no trace of the earth, I was 

 led, in the next place, to try whether this might be owing merely to the inso- 

 lubility of the substance in question ; for which reason I varied the experiment 

 by watering my plants with a weak solution of nitrate of strontian. 



It will appear from the subsequent details, that in either form of the experi- 

 ment lime, and not strontites, was the earth that presented itself; but as in 

 proportion to the care that had been taken to exclude any external source of 

 supply for earthy matter, the quantity obtained from the ashes grew less and 

 less, it would be rash to infer, from the small excess of lime which was de- 

 tected, any power belonging to the plant of forming it, when not supplied 

 from without. 



Should it, however, appear that a vegetable, which, though not perhaps in 

 full vigour, was at least in a growing and healthy condition, remained in con- 

 tact with strontian, both in the state of sulphate, and likewise in that of ni- 

 trate dissolved in water, for months together without absorbing any portion, 

 and that, although in want of earthy matter, as its laxity of fibre evidently 

 betrayed, the conclusion would seem to follow, that plants have to a certain 

 extent the power, as living agents, of rejecting such substances as, without 

 being poisonous, are unusual to them, and probably unfitted for their oeconomy 

 and structure. 



Omitting some previous experiments, of which I have preserved no correct 



