SAP OF TREES DURING WINTER. 115 



composition of the leaf : for we have abundant reason to believe that this 

 organ is the principal agent of assimilation ; and scarcely anything can 

 be more contrary to every conclusion we should draw from analogical 

 reasoning and comparison of the vegetable with the animal economy, or 

 in itself more improbable, than that the leaf, or any other organ, should 

 singly prepare and assimilate immediately from the crude aqueous sap 

 that matter which composes itself. 



It has been contended * that the buds themselves contain the nutriment 

 necessary for the minute unfolding leaves : but trees possess a power to 

 reproduce their buds, and the matter necessary to form these buds must 

 evidently be derived from some other source ; nor does it appear probable 

 that the young leaves very soon enter on this office, for the experiments 

 of Ingenhouz prove that their action on the air which surrounds them is 

 very essentially different from that of full-grown leaves. It is true that 

 buds in many instances will vegetate, and produce trees, when a very 

 small portion only of alburnum remains attached to them ; but the first 

 efforts of vegetation in such buds are much more feeble than in others to 

 which a larger quantity of alburnum is attached, and therefore we have, 

 in this case, no grounds to suppose that the leaves derive their first 

 nutriment from the crude sap. 



It is also generally admitted, from the experiments of Bonnet and 

 Du Hamel, which I have repeated with the same result, that in the 

 cotyledons of the seed is deposited a quantity of nutriment for the bud 

 which every seed contains ; and though no vessels can be traced -|- which 

 lead immediately from the cotyledons to the bud or plumula, it is not 

 difficult to point out a more circuitous passage, which is perfectly similar 

 to that through which I conceive the sap to be carried from the leaves 

 to the buds in the subsequent growth of the tree ; and I am in possession 

 of many facts to prove that seedling trees, in the first stage of their 

 existence, depend entirely on the nutriment afforded by the cotyledons ; 

 and that they are greatly injured, and in many instances killed, by being 

 put to vegetate in rich mould. 



We have much more decisive evidence that bulbous and tuberous 

 rooted plants contain the matter within themselves which subsequently 

 composes their leaves ; for we see them vegetate even in dry rooms on 

 the approach of spring ; and many bulbous rooted plants produce their 

 leaves and flowers with nearly the same vigour by the application of 

 water only, as they do when growing in the best mould. But the water 



* Thomson's Chemistry. f Hedwig. 



i 2 



