on Gardening and Rural Affairs, 79 



They are the lymphatic tubes of Decandolle, the false tracheae of Mirbel, 

 and the corpusculiferous tubes of our author. They are not found in the 

 bark, nor in the pith, and it is well known that the sap does not rise 

 through these parts of the stem. 



The proper juice, or sap, after it has been changed by the leaves into a 

 nutritious fluid, according to M. Dutrochet, descends both by the bark and 

 the alburnum or soft wood, through tubular oblong' cells. These oblong 

 cells give out the nutritive juice contained in them through their sides, and 

 in spring, when the sap ascends, it takes up a portion of this juice for the 

 developement of the leaves and the growth of the plant. The pith neither 

 has the power of conducting the ascending or descending sap. M. Dutro- 

 chet agrees with Linnaeus, Dr. Darwin, and others, in considering it to be 

 to the vegetable, what the brain and spinal marrow are to the animal. Dr. 

 A. T. Thomson {Lectures on Botany, vol. i. p. 579.) conjectures that the 

 pith is intended chiefly to give bulk and stability to the young shoot ; be- 

 cause, whenever this becomes ligneous and able to support itself, the pith 

 dries up and diminishes in volume rather than increases. 



Besides the vessels for the ascent of the sap, and those for the descent of 

 the proper juice, there are a third description of vessels, which radiate from 

 the centre of stems to their circumference, and are commonly called medul- 

 lary rays. These rays are composed of oblong tubes or cells, extending 

 from the centre of the wood to the bark, where they are met by similar 

 tubes, in apparent but not real continuity in the bark. The radiated tracheae 

 of the wood give out the ascending sap from the lymphatic tubes, and the 

 radiating vessels of the bark give out the prepared sap, or proper juice, from 

 the descending tracheae, or oblong cells, of the bark. The juice and the sap, 

 thus poured out between the wood and the bark, unite in forming a nutri- 

 tive fluid, which, consolidating, adds to the bulk of the plant, in the form of 

 alburnum or soft wood, and liber or inner bark. This, it must be acknow- 

 ledged, is a very simple and beautiful theory, and altogether consistent with 

 matter of fact. 



The next point which M. Dutrochet proceeds to determine is, the cause 

 of the progression of the sap in the lymphatic tubes, oblong cells, and 

 radiating tracheae. It is unnecessary to trace the proofs that there is no 

 actual circulation of the sap in plants, but merely an ascending and descend- 

 ing current, and a lateral diffusion and union. The condition of a plant 

 requisite to admit of the exercise of these functions is, the susceptibility of 

 becoming turgid by the application of water ; in other words, that which 

 distinguishes a dead plant from a living one is, the turgidity of its cellular 

 parts. A dead plant may have its tubes, cells, and tracheae filled with fluid, 

 but these will never become turgid : a living plant, on the contrary, which 

 has been apparently dead, when one extremity is placed in fluid, becomes 

 filled with it throughout to an excess productive of turgidity. In a sepa- 

 rated part of a plant, the ascension of the sap depends on the susceptibility 

 of turgidity of all the parts of the section. In a plant growing in the soil, 

 the cause of turgidity, or of the rise of the sap, is to be found in the minute 

 conical bodies which terminate each radicle. M. Dutrochet, by careful 

 examination with a microscope, found that the minute conical termination 

 of the radicle was furnished with other projecting bodies, like sponges, 

 which perform the office of the piston of a syringe, and have the power of 

 introducing into their cavity, and through their sides, the water which 

 comes in contact with their exterior surface, and which, at the same time, 

 opposes the exit of any fluid these spongioles imbibe. To this power M. 

 Dutrochet has applied the term endosmose (endon, inward, osmos, impulse) ; 

 and he has proved its existence, on a larger scale, in the coecum or blind 

 gut of a young chicken, which he filled half full of milk, firmly closed at 

 the open extremity, and then immersed in water. At the end of twenty- 



