262 Dr. Daubeny o» the Degree of Selection exercised hi/ Plants, witli regard 



In other respects the results indicate decisively a connexion between the 

 quantity of earthy matter contained in the plant, and the readiness with which 

 it is supplied with it from without ; since, even if we confine ourselves to the 

 ])ortions above ground, where there can be no suspicion of any foreign ad- 

 mixture, it will be seen that the largest amount of calcareous earth was 

 obtained from the straw which had grown up in Carrara marble, and that the 

 excess of it over that in the seeds was in the other instances but inconsi- 

 derable. 



The last experiment of the kind I shall allude to was made in the present 

 year. 



Two boxes only were this time employed, the one filled with sea-sand, the 

 other with Carrara marble. In each of them 500 grains of barley were planted; 

 they were watered, as before, with a weak solution of nitrate of strontian, and 

 were protected from dust and rain by being placed under cover in a greenhouse. 

 The plants obtained, being burnt, were treated in the same manner as before, 

 and rigorously examined for strontian. Of this, the roots of both samples 

 appeared to contain a trace, though the largest amount did not exceed -rVth of 

 a grain. On the other hand, the parts which were above the surface, and 

 therefore free from all contact with the soil, appeared to be entirely desti- 

 tute of this earth. Nevertheless every portion, both of the sand and of the 

 Carrara marble, was found impregnated with the nitrate of strontian that 

 had been held in solution by the water with which the plants had been moist- 

 ened. 



I fear the conclusions that may be legitimately deduced from the above 

 experiments will hardly be deemed of sufficient novelty and importance to 

 repay the labour and time they have cost me; since, in so far as the main 

 point is concerned, they serve only to confirm in an indirect manner the con- 

 clusion, which both analogy and experiment concur in establishing, namely, 

 that if plants do in some cases obtain fixed principles which cannot be traced 

 to any external source, yet the quantity of such substances which enters into 

 their system is always less in proportion to the pains taken to cut off a supply. 

 Hence the inference would seem to be, that the indications of a contrary de- 

 scription that sometimes present themselves are fallacious, resulting from the 



