On the Actmi of detached Leaves of Plants. 347 



mature leaves might be miide to nourish and promote the growth 

 of immature leaves, without the aid of roots. Several shoots of 

 the vine, each about a yard long, were detached from the trees, 

 and laid over a succession of basins of water, into which each 

 of the mature leaves was in part depressed : and thus circum- 

 stanced, the voung leaves continued to grow, and the points of 

 the shoots to elongate; and all were alive and in perfect ap- 

 parent health at the end of a month. I'lie water necessary to 

 preserve t'le young leaves must in this case have been derived 

 from the mature leaves ; and I entertain no doubt, but that the 

 organizablc matter which occasioned tlieir growth, was derived 

 from the same source. Intersection of the Iiark l>etween the 

 mature and young leaves was not attended v/ith any injurious 

 consequences, and the sap must, therefore, have passed to tlie 

 young leaves thiough the alijurtmrn. 



CJonsistentiv v.itli the preceding circumstances, if the mature 

 leaves be destroyed, or taken off, t!ie fruit ceases to grow, or. if 

 full grown, remains witlinut richness or flavour ; and the power 

 of feeding fruits in winter and early spring seems to be confined 

 to everiireen plants. The orange and lemon tree, the ivy and 

 holly, afford familiar CKarnples of this ; and where a genus of 

 plants consists of evergreen and deciduous specie*, as that of 

 mespilwi and vihirnum, tiie evergreen species alone nourish 

 their fruit in winter and early spring. 



The probable passage of t!ie sap from the mature to the young 

 IrJives and fruit may, I think, ije easily pointed out, though de- 

 cisive proof of its course will probabh/ never be adduced. Having 

 often detached the bark from the alburnum vi' the stems of 

 youug oaks, just at the period when the midsummer shoots were 

 beginning to elongate, I observed, as others have done, that a 

 liuid exuded from those parts of the surface of the alburnum, 

 v/hich are called (most improperly) the medullary processes, and 

 from correspondent points of the bark, which resemble the me- 

 dullary processes in organization. This fluid has been proved, 

 by its power of rapidly generating an organic substance, to be 

 the true sap of the tree, part of which I conceive at this period, 

 to be passing from the bark to join tlie ascending current in the 

 alburnum ; which current feeds the young succulent shoots and 

 growing leaves. Subjecting the alburnum to a slight degree of 

 pressure at this period, I found that a considerable quantity of 

 liquid, being apparently the true sap of the tree, issued out la- 

 terally through the medullary processes, as well as longitudinallv 

 througii the cellular substance of the alburnum : but the tubes 

 of it continued empty, and their position was marked by de- 

 pressions of the surface of the extravasated fluid. I endeavoured 

 to ascertain, what prcportion of water a given quantity of the 



alburnum 



