146 Circulating System of Plants. 



the real natural course of the vegetable fluids. It may be 

 said that the analogy does not hold good throughout, because 

 some cuttings of plants will grow, and become plants; therefore, 

 that the circulating principle is not destroyed. I admit the 

 objection, but maintain, that, although the vital principle may 

 be retained, it is only in the buds, or parts allied to buds in 

 their nature, each of which is, as it were, a separate system of 

 life ; and that the interrupted motion of the vital fluids is never 

 really restored, till one or more of these vital germs developes 

 itself in the protrusion of leaves and roots. This would form a 

 most interesting subject for a future paper. 



I would finally suggest, that if we ever expect to determine, 

 beyond a question, the channels of the vegetable currents, we 

 must operate upon living subjects ; and to do this, a course 

 of experiments, something like the following, might be under- 

 taken : — Two or more young plants with very transparent 

 stems, the balsam for instance, might be selected. Let one of 

 these, growing in a small pot, be watered on all occasions with 

 an infusion of Brazil-wood, logwood, or of the skins of black 

 grapes or currants ; and let another plant be taken up, and 

 its roots kept in any similar coloured infusion. If upon in- 

 spection (by the microscope) of the stems uninjured, or even 

 after cautiously removing the epidermis (cuticle), or a portion 

 of the stem longitudinally, any of the colouring matter be 

 found within the tubes or cells, and especially if it pervade any 

 determinable part of the ramifications of the leaf-stalks, then, 

 a conclusive result may be anticipated ; and other experiments, 

 repeatedly varied and accurately noted, may lead to a general 

 theory founded upon facts. 



But till some such experiments be carefully instituted and 

 recorded (I purpose to make the foregoing experiments my- 

 self during the approaching spring), we must, I fear, be con- 

 tent to avow, with Mr. Burnett, that " with so few facts as we 

 at present possess, it would be dangerous to generalise ; and 

 when we consider the very minute portions that can be sub- 

 mitted to examination, I do not think that the whole theory 

 of the circulation is a point that will readily be settled." 



It is but just, however, to add, that Mr. Knight (judging 

 from one or more of his direct statements to me) has micro- 

 scopically investigated many living growing plants ; and, with 

 the most patient assiduity and minute accuracy, has dissected 

 their integuments, and laid bare their internal structure : and 

 I now avow, that from his statements, compared with my own 

 observations, I see no sufficient reason to doubt that the real 

 and regular conduits of the ascending sap are the cells (a part 

 of them at least) of the alburnum; that the elaborated fluids 



