Linnccan Society. 53 



ment with the hope of ascertaining by more decisive experiments 

 than had been hitherto done, whether plants are able under any 

 circumstances to form those earthy and alkaline matters which they 

 usually contain, when not supplied with them from without. 



With this view, he planted a known weight of the seeds of certain 

 vegetables in earths of known composition, introduced in a finely 

 divided state into boxes cased internally with sheet zinc. One box, 

 containing each kind of earth, was placed in a garden exposed to 

 rain and dust, and a corresponding one of each kind in a greenhouse 

 protected from both. 



The earths employed were, washed sea-sand, Carrara marble and 

 sulphate of strontian. 



The crop obtained from each of the boxes was separately burnt, 

 and the ashes weighed and examined chemically. That from the 

 boxes placed in the garden was greater than that from those in the 

 greenhouse; hut in both cases an increase of earthy matter was ob- 

 served beyond that which existed in the seeds from which they had 

 sprung. 



Having remarked, however, that the plants grown in strontian 

 contained none of that earth, he resolved to try whether this cir- 

 cumstance might be owing merely to the insolubility of the sulphate 

 in water, or to some specific power belonging to the plant of re- 

 jecting the earth in question. 



He therefore varied the experiment the succeeding year, by 

 planting the seeds in four different soils, namely, sand, marble, sul- 

 phate of strontian and flowers of sulphur, and watering them with a 

 weak solution of nitrate of strontian. In every instance there was 

 an increase of calcareous matter, beyond that present in the seeds, 

 greatest in the plants that had grown in sulphate of strontian and in 

 Carrara marble, least in those planted in sulphur; but the largest 

 quantity of strontian ever detected by chemical means from their 

 ashes did not exceed 0-4 of a grain. From these and similar ex- 

 periments, detailed in the memoir, the author concludes, that the 

 absorbing surfaces, or spongioles, of the roots of plants either do 

 not admit strontian earth at all, even in a state of solution, or at 

 least receive it much less readily than they do calcareous matter. 



He details an experiment to show, that the absence of strontian 

 from the solid parts of the plants was owing to its remaining unab- 

 sorbed by the roots, not to its being excreted by them; and ac- 

 counts for the difference between what happened in the instance of 

 the strontian, and that which he had himself observed in common 

 with Mons. de Saussure, as holding good with regard to solutions of 

 substances more directly injurious to the plant, by supposing, in the 

 latter instance, the spongioles to be disorganized by the poisonous 

 quality of the substance, and consequently to have allowed the so- 

 lution to be absorbed by capillary attraction. In this latter case 

 he observed, that before the plant is destroyed, a portion of the 

 poisonous substance will be excreted again by the spongioles of 

 the roots. 



Upon the whole he concludes, that his experiments lend no coun- 

 tenance to the idea that plants can form their earthy constituents 

 v.lun not supplied with them from without, although they do not 

 altogether demonstrate the reverse. 



