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172 On the Selecting Power of' Plants 



solved was chiefly composed of* an earthy carbonate and phos- 

 phate. Now I satisfied myself, by a minute examination, that 

 the acid solution derived from the stems contained no trace 

 whatever of strontian, although a small portion appeared to be 

 present in, or at least adherent to, the roots. 



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 with- 

 out ; since, even if we confine ourselves to the portions above 

 ground, where there can be no suspicion of any foreign admix- 

 ture, 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 inconsiderable. 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 one-tenth of a grain. On the 

 other hand, the parts which were above the surface, and there- 

 fore free from all contact with the soil, appeared to be entirely 

 destitute 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 moistened. 



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 conclusion, 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 



