Circulating System of Plants. 145 



*'The medullary processes (as they have been misnamed) are 

 formed convergently from the bark, not divergently, as I have 

 demonstrated in the Philosophical Transactions. They are 

 permeable to fluids ; for when the bark is taken off in spring, 

 a fluid is seen to exude from them, which, under favourable 

 circumstances, will become perfect bark. The spiral tubes, 

 when full grown, certainly contain no fluid ; that is, nothing 

 but air." 



When I wrote the three treatises on vegetable physiology 

 in the Domestic Gardcjier's Manual, I was impressed by the 

 weight of some of the authorities that I had been perusing; 

 and, combining the facts stated with others derived from my 

 own microscopic observations, I became partially convinced 

 that in the tubular system of plants were to be found the real 

 channels of, at least, the ascending sap. 1 had, indeed, 

 detected fluids in the longitudinal tubes of some herbaceous 

 plants, as, for instance, the tulip, wild hyacinth (5cilla nutans), 

 and the like. In these, 1 clearly observed one or more bub- 

 bles of air interposed between portions of fluid, by which the 

 latter was rendered more distinctly apparent. I had also 

 noticed the partial ascent (or rather the diifusion) of coloured 

 liquids through those portions of the longitudinal, semi-opaque 

 masses, that physiologists had stated to be the ascending sap- 

 vessels ; but I was invariably disappointed in every attempt 

 to introduce such colouring matter into the vessels of the 

 leaves, by placing the lower extremities of young shoots in 

 coloured infusions ; although they remained therein for twenty- 

 four, or thirty-six hours, and even, at times, exposed to the 

 stimulus of a moderate heat. Facts and reiterated observ- 

 ations led me, therefore, to doubt the accuracy of many re- 

 corded experiments ; and to question the philosophy of any 

 inference, however plausible it might appear, which had been 

 drawn from the investigation of mutilated parts of an organised 

 being, that previously had been actuated by the vital principle. 

 These doubts, and also a variety of queries that naturally 

 suggested themselves, I stated in a paper which was read at a 

 meeting of the London Horticultural Society, Jan. 18. 1831. 



We ought not to deceive ourselves in our researches after 

 truth. A detached dissected portion of a plant may exhibit 

 apparent motion in the fluids it retains, it may also absorb the 

 colouring matter of an infusion ; but, surely, it would be as 

 unreasonable to expect that an anatomist should demonstrate 

 the natural circulation of the blood through the arteries and 

 veins of a limb, deprived by amputation of the propulsive 

 energy of the heart, as to believe that a detached and lacerated 

 joint of a root or stalk could furnish undoubted evidence of 



Vol. VIIL — No. 37. v 



