20G NUTRIMENT OF 



through the cell walls of the fibrils. A solution, therefore, must be perfect ; and all such so- 

 lutions may be received into the tissues, and pass the cells ; it makes no difference whether the 

 solution is nutritive or poisonous, it passes in : if poisonous, or in other words, if it affects the 

 cell wall chemically, as solutions of corrosive sublimate or arsenic would do, the plant is de- 

 stroyed ; it has no selecting power, no discrimination of what is good or bad. In order to 

 be taken up the matter must be perfectly dissolved. It is hovi'ever supposed by Muldek, that 

 the roots have, in their endosmotic power, different relations to the matters absorbed ; so that 

 some substances are more readily absorbed than others. The fact is undoubtedly true that 

 some substances are more readily taken uj) ; whether however the power denominated endosmose 

 is the power, admits of a doubt. There is a dislike to the idea that a mere dead membrane is 

 competent to the performance of the functions under consideration. There is, however, much 

 in the doctrine which is plausible ; and the illustration which endosmose furnishes to the promo- 

 tion of the circulation, is well worthy of a notice, as one of the probable forces concerned in 

 the circulation of the saps in vegetables. 



NUTRIMENT OF OKGANIZED BODIES, 



There is no necessity in maintaining the opinion that plants are endowed with an extraor- 

 dinary power for selecting nutriment, and of rejecting matters injurious to them : the original 

 constitution of the rocks, and the adaptation of plants to the soil, do not require this ; although 

 the matters of the soil are heterogenous, still there are so few elements which are injurious to 

 them, that the power of rejecting those would be of little or no consequence. All plants are 

 furnished with the same elements; then whatever differences we may observe in the vegetable 

 productions must be ascribed to the combining and modifying powers of each individual species. 

 The stem of a plant differs, in composition, from the leaf, and the chaff from the grain ; not 

 because the root made a special selection of materials from the great store house, the soil, but 

 because each part is fitted to arrange and combine the matters taken up by the root, in its own 

 way and according to its peculiar structure. There is a remarkable difference in the growth of 

 plants and animals : the latter undergo a continual waste of their organs during their whole 

 period of existence ; this waste is the most rapid during the period of its most rapid increase : 

 plants undergo no waste, properly speaking, though it was supposed by many physiologists 

 at one time, that the extraneous matter, or waste, was rejected by the roots, and cast forth into 

 the soil. This view of the waste of plants finds but few advocates now. The only waste which 

 plants suffer is from exhalation of water from their leaves, or from their general surfaces. The 

 injurious or poisonous matters, either to plants or animals, are confined to narrow veins in the 

 rocky strata j hence they can really exert no influence on vegetation in general. There is 

 but one exception to this ; the proto-salts of iron exert an injurious influence upon plants. 

 This salt is formed by the decomposition of pyrites, diffused through some of our common 

 rocks : this salt, after all, is rarely in such quantities as to require much attention ; it is easily 

 disposed of by lime, being in its turn decomposed, the sulphuric acid of the sulphate of iron 

 going over to the lime and forming gypsum or sulphate of lime. 



