Q2 fclkCULATlON OF THE SAp. 



many advantages, both as a gardener and farmer, (partlctilarly 

 in the management of fruit and forest trees,) from the expe- 

 riments which have been the subject of my former memoirs, 

 that I am confident much public benefit might be derived from 

 an intimate acquaintance with the use and office of the various 

 organs of plants ; and thence feel anxious to adduce facts to 

 prove that the conclusions I have drawn are not inconsistent 

 w^ith the facts stated by my great predecessors. 

 The first mo- It has been acknowledged, I believe, by every naturalist 

 lion of the true ■who has w^ritten on the subject, (and the fact is indeed too 

 ^uon fs"^"^^" obvious to be controverted,) that the matter which enters info 

 downwards the composition of the radicles of germinating seeds existed 

 previously in their cotyledons ; and as the radicles encrease 

 only in length by parts successively added to their apices, or 

 points most distant from their cotyledons, it follows of neces- 

 sity that the first motion of the true sap, as this period, is 

 downwards. And as no alburnous tubes exist in the radicles 

 of germinating seeds during the earlier periods of their growth, 

 the sap in its descent must either pass through the bark, or 

 the medulla. But the medulla does not apparently contain 

 any vessels calculated to carry the descending sap ; whilst 

 —through the the cortical vessels are, during this period, much distended and 

 bark. full of moisture : and as the medulla certainly does not carry 



any fluid in stems or branches of more than one year old, it 

 can scarcely be suspected that it, at any period, conveys the 

 whole current of the descending sap. 

 Cortical vessels As the leaves grow, and enter on their office, cortical ves- 

 from the bases ^q]^^ jjj every respect apparently similar to those which des-> 

 by which the' cended from the cotyledons, are found to descend from the 

 sap descend, bases of the Leaves ; and there appears no reason, with whieh I 

 am acquainted, to suspect that both do nof carry a similar fluid, 

 and that the course of this fluid is, in the first instance, always 

 towards the roots. 

 The ascending The ascending sap, on the contrary, rises wholly through 

 sap passes the alburnum and central vessels ; for the destruction of a 

 alburnum a^nd portion of the bark, in a circle round the tree, does not imme- 

 central vessels, diately in the slightest degree check the growth of its leaves^ 

 and branches : but the alburnous vessels appear, from the 

 experiments 1 have related in a former paper,* and from those 



* PhiUTrans. for 1804. 



