Comparative Physiology. 511 



to secretion or assimilation. The absorbents, or especially the 

 absorbing glands, of animals have been thought to produce some 

 changes on the chyle, but this seems uncertain ; and these vessels 

 appear to be endowed with more sensibility than those of plants. 

 The power of endosmose seems similar to that described as hy- 

 groscopicity by DeCandoUe, but more intimately and fully exa- 

 mined by Dutrochet. It is stated by DeCandolle, Muller, and 

 others, that the connexion of endosmose with electricity, which 

 Dutrochet fancied he had made out, has not been confirmed ; it 

 is probable, however, from the connexion of electricity ge- 

 nerally with all action, that it will be concerned either as cause 

 or effect. Some have attributed the power to a compound and 

 greater attraction subsisting in a dense fluid from its more 

 compound nature, than in a fluid comparatively more simple; 

 others say that the tissue of the bladder has more attraction for 

 some substances than others, and causes those substances to be 

 longer in passing through the pores. Di% Carpenter seems to 

 be something of this opinion. Saussure, who made many expe- 

 riments on this subject, was of opinion that they passed more or 

 less quickly according to their liquidity, which would mecha- 

 nically allow of their passing the pores more easily. Professor 

 Thomson* objects to this, that more water would require to be 

 absorbed ; the quantity of water absorbed by plants under proper 

 circumstances ss, however, so great as to modify this objection ; 

 the thinner the fluid it should certainly pass the more easily, 

 and, if we suppose the operations of nature to be conducted on 

 the most j)erfect plan, the membrane set apart for absorption 

 should not have that faculty interfered with by another che- 

 mical power possessed by the same organ. Vogelf found in his 

 exjDeriments that most plants, if supplied at the roots with an 

 unhmited quantity of saline substances in solution, would absorb 

 so much, even of those found beneficial in smaller quantities, such 

 as nitrate of ]5otash, &c., as to cause death. The sulphate of 

 copper he found, like Saussure, most rapidly absorbed ; and this 

 and others partially decomposed, by the abstraction of oxygen 

 reducing the salt to the state of a protosulphate ; other saline 

 substances were found unaltered after death. He found that 

 chara and some other plants would not absorb the salts of 

 copper ; this he attributes to their containing much carbonate of 

 lime, but it is probably owing to the peculiar formation of the 

 invisible pores, which all absorbing membranes are supposed to 

 possess. Capillary attraction is thought to assist in absorption 

 by furthering the ascent or I'emoval of the imbibed fluid, so as 

 to allow the denser descending sap to renew the phenomena of 



* Thomson's Organic Chemistry of Vegetables, p. 974. 

 t Gardeners' Chronicle, May 23. 1843. 



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