DIRECTION OF THE GROWTH OF ROOTS, olo 



«f each pot, so as to prevent both the mould and the seeds 

 falling out, in whatever position the pots might be placed: 

 and the bars were so disposed, as not at all'to interfere 

 with the radicles of the seeds, when protruding. The pots 

 were then directly inverted : and the seeds were conse- 

 quently placed beneath the mould; but each seed was so far 

 depressed into the mould, as to be about half covered : by 

 which means each radicle, when first emitted, was in con- 

 tact with the mould above, and the air below. Water was 

 then introduced through the bottom of the inverted pot, in 

 sufficient quantity to keep the mould moderately moist; and, 

 the pots being suspended from the roof of a forcing house, 

 the seeds soon vegetated. 



In former experiments*, wherever the seeds were placed The radicles 

 to vegetate at rest, the radicles descended perpendicularly ^^^^j"„^ ^^2' 

 downward, in whatever direction they were first protruded ; shot up fibres 

 but under the preceding circumstances they extended hori- 

 zontally along the surface of the mould, and in contact with 

 it; and in a few days emitted many fibrous roots upward 

 into it; just as they would have done, if guided by the 

 instinctive faculties and passions of animal life ; aud as I 

 concluded before I made the experiment that they would 

 do, under the guidance of much more simple laws, the mode 

 of operating of which I shall endeavour to explain. 



Whatever be the machinery, by which the sap of trees Ascending say 

 is raised to the extremities of their branches, it is obvious, jj^^j^*^';"^^™*' 

 that this machinery is first put into action by the stems and stems; ami 

 branches, and not by the roots ; for the graft or bud, when- '"'^^'^'^^''> 

 ever it has become fully united to the stock, wholly regu- 

 lates the season and temperature, in which the sap is to be put 

 in motion, in perfect independence of the habits of the 

 stock ; whether these be late or early. If all the branches an<J the qnan- 

 ofatree, exclusive of one, be much shaded by conuguous t^^r'^^i^j^^j^yj^'^ 



trees +, or other objects, the branch which is exposederaploy it, to 

 ten the light attracts to itself a large portion of the ascend- ^ 

 ing sap, which it employs in the formation of leaves and 



* Phil. Trans. 1806, p. 1 : or Journal, vol. xiv, p. 4t)9. 

 t Phil. Trans. 1805 and 1809 : or Journal, vol, xii, pp. 233, 308 ; 

 vol. XXV, p. 118. 



•vigorous 



