170 ON THE ACTION OF DETACHED LEAVES OF PLANTS. 



of the mature leaves of young plants not only suspended the growth of 

 the roots, but also the growth of the immature leaves ; whence I inferred, 

 in a former communication, that the organisable matter which composes 

 the young leaves has always undergone a previous preparation in other 

 leaves of the plant, either of the same or preceding season ; and I was 

 thence led to expect that, under favourable circumstances, the mature 

 leaves might be made 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, arid laid over a succession 

 of basins of water, into which each of the mature leaves was in part 

 depressed ; and thus circumstanced, the young leaves continued to grow, 

 and the points of the shoots to elongate ; and all were alive, and in 

 perfect apparent health, at the end of a month. The water necessary to 

 preserve the young leaves must in this case have been derived from the 

 mature leaves ; and I entertain no doubt but that the organisable matter 

 which occasioned their growth was derived from the same source. Inter- 

 section of the bark between the mature and young leaves was not attended 

 with any injurious consequences, and the sap must, therefore, have passed 

 to the young leaves through the alburnum. 



Consistently with the preceding circumstances, if the mature leaves be 

 destroyed, or taken off, the fruit ceases to grow or, if full grown, 

 remains without richness or flavour ; and the power of feeding fruits in 

 winter and early spring seems to be confined to evergreen plants. The 

 orange and lemon tree, the ivy and holly, afford familiar examples of this ; 

 and where a genus of plants consists of evergreen and deciduous species, 

 as that of mespilus and viburnum, the evergreen species alone nourish 

 their fruit in winter and early spring. 



The probable passage of the sap from the mature to the young leaves 

 and fruit may, I think, be easily pointed out, though decisive proof of its 

 course will probably never be adduced. Having often detached the bark 

 from the alburnum of the stems of young oaks, just at the period when 

 the midsummer shoots were beginning to elongate, I observed, as others 

 have done, that a fluid exuded from those parts of the surface of the 

 alburnum which are called (most improperly) the medullary processes, 

 and from correspondent points of the bark which resemble the medullary 

 processes in organisation. 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 the ascending current in the alburnum ; which current feeds the 

 young succulent shoots and growing leaves. Subjecting the alburnum 



