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ON VEGETABLE NUTRITION. 



I perceive in the last number of your interesting periodical (No. x., for July, 

 p. 225) a question proposed by one of your correspondents, as to whether " the 

 fluid absorbed by capillary attraction by the spongioles or rootlets of plants be 

 conveyed to the leaves by the same means (capillary attraction), or by some 

 vital principle in the plant ?" I hope that, if his object be to obtain the pre- 

 sent most probable opinions on a disputed point, without the trouble of diving 

 through all the pages usually allotted to such discussions in botanical works, 

 which discussions indeed are often more curious than useful, I shall not be 

 thought to be intruding on your pages by condensing, as far as lays in my 

 power, what I have seen in one or two modern books on the subject, particu- 

 larly from that of Professor Henslow, as at once cheap and within the reach of 

 every individual. Should he, however, require new facts in proof of his own 

 opinions, some other more erudite of your correspondents may perhaps satisfy 

 him on that point. 



That the conveyance of sap absorbed by the spongioles or rootlets to the 

 leaves, is at all the effect of capillary attraction, has of late years been ques- 

 tioned by various authors, and Dr. Arnott, in his Elements of Physics (art. 

 Capillary Attraction), says that the raising of the sap from the roots of vege- 

 tables " is known now to be chiefly an action of vegetable life." That the vital 

 force alone is the cause of its ascent, is, however, on the other hand, by no means 

 probable, and the opinion of De Candolle — who supposes it to be propelled along 

 the intercellular passages by successive contractions and dilatations of the cells — is 

 now, for very obvious and well-grounded reasons (as the same opinion is also in 

 the case of the propulsion of the blood through the arteries and veins), for the 

 most part exploded. The spongioles, moreover, have not only the power of ab- 

 sorbing, but also of propelling the fluid imbibed by them with considerable force ; 

 and it has been supposed, from the analogy of the results of this action with 

 those of endosmose — or that property of both animal and vegetable membrane of 

 allowing fluids of different density on the opposite sides of it to pass through, and 

 thus intermix until the density of both be equal — that the propulsion of the sap 

 might be partly at least attributable to this action going on between the denser 

 fluids contained in the vesicles of the spongioles and surrounding fluids, and thus 

 that both its absorption and propulsion may be principally referred to mechanical 

 causes. However this may be, certain it is that the vital force itself holds an 

 important station in this as well as the other operations of vegetable economy, 

 although in the case of absorption by the spongioles its effects are not so evident 

 from experiment ; and the ease with which fluids are absorbed, depending more 



