316 Stale in u hlch the true Sap of Trees 



they have aflTordccl nutriment to a crop of seed, we may 3us-r 

 pect that a tree, which has borne much fruit in one season, 

 becomes in a similar way exhausted, and incapable of af- 

 fording proper nutriment to a crop in tlie succeeding year. 

 And I am mucii inchned to believe that were the wood of a 

 tree in thi? state accurately weighed, it would be found spe- 

 cifically lighter than that of a similar tree, which had not 

 afforded nutriment to fruit or blossoms, in the preceding 

 year, or years. 



If it be admitted that the substance which enters into the 

 composition of the first leaves m the spring is derived from 

 matter vk'hich has undergone some previous preparation within 

 the plant, (and I am at a loss to conceive on what grounds 

 thi.'* can be denied, in bulbous and tuberous rooted plants 

 at least,) it must also be admitted that the leaves which are 

 2;enerated in the summer derive their substance from a simi- 

 lar source ; and this cannot be conceded without a direct 

 admission of the existence of vegetable circulation, which is 

 denied by so many eminent naturalists. I have not, how- 

 ever, found in their writings a single fact to disprove its 

 existence, nor any great weight in their arguments, except 

 those drawn from two important errors in the admirable 

 works of Hales and Du Hamel, which I have noticed in a 

 former memoir. I shall therefore proceed to point out the 

 channels, through which I conceive the circulating fiuids to 

 pass. 



When a seed is deposited in the ground, or otherwise ex- 

 posed to a proper degree of heat and moisture, and exposure 

 to air, water is absorbed by the cotyledons, and the young 

 radicle or root is emitted. At this period, and in every 

 subsequent stage of the growth of the root, it increases in 

 length by the addition of new parts to its apex, or point, 

 and not by any general distension of its vessels and fibres ; 

 and the experiments of Bonnet and Du Hamel leave little 

 grounds of doubt, but that the new matter which is added 

 to the point of the root descends from the cotyledons. The 

 first motion therefore of the fluids in plants is downwards, 

 towards the point of the root ; and the vessels which appear 

 to carry them, are of the same kind with those which are 

 subsequently found in the bark, where I have, on a former 

 occasion, endeavoured to prove that they execute the same 

 office. 



In the last spring I examined almost every day the pro- 

 gressive changes which take place in the radicle emitted by 

 the horse chesnut : I found it, at its first existence, and 

 until it was some weeks old, to be incapable of absorbing 



coloured 



