542 New Theory of the Ascent of the Sap. 



that now not a single ray remains, not even the shadow of a 

 hope, to give encouragement to future researches. Nature, 

 indeed, seems to throw an impenetrable veil over the mysteries, 

 and guard with a jealous care the theory of vegetable form- 

 ation. 



After such disheartening results, any farther attempt to 

 illustrate this subject might appear but lost labour ; but it is the 

 business of the philosopher to be checked by no difficuUy 

 that may be interposed between him and the object of his 

 research; and, at the same time, to conceive nothing inex- 

 plicable, which has not yet received a probable explanation. 

 Under the influence of such feelings, I have placed together the 

 following hints, which, should they be thought of sufficient 

 importance, may perhaps engage the attention of some of your 

 readers, who probably may have better opportunities of con- 

 ducting such enquiries than myself. 



What appears to me of great weight in this theory is, that 

 it is founded on nutrition, and consequently dependent on 

 the vital principle ; an argument against which many of the 

 abandoned theories could make no stand. 



The theory I wish to prove is the following : — The sap, 

 in its ascent in the stem, becomes deprived of some of its 

 constituents, more especially of its aqueous part ; this depriv- 

 ation is effected by the vital principle of the plant decom- 

 posing the aqueous part, and assimilating the resulting gases 

 to its own constituents. As the assimilation takes place, a 

 partial vacuum is formed by the change of gases to a solid 

 form ; and this vacuum is immediately filled, by the sap 

 rushing into it, according to the well known law of the tend- 

 ency of fluids to rush into any cavity deprived of the pre- 

 sence of air. 



In order to strengthen this theory, it is necessary to bring 

 forward some arguments which prove the changes the sap 

 undergoes in the stem, and also to prove, that some of its 

 elements are there appropriated to its growth. 



It is now received on all sides that the sap ascends through 

 the wood, and in greater quantity in the newest layers ; in 

 fact, so true is this, that in the innermost layers, where the 

 vessels have become gradually obstructed by the deposition 

 of ligneous matter, vitality in time ceases, and they decay 

 away, as we see in very old trees, where the internal part has 

 been quite removed, and an external tube now serves to carry 

 on the functions of the tree. Here the vessels become 

 gradually hardened, and in the course of time perfectly ob- 

 structed, by the deposition of matter resulting from the de- 

 composition of some of the aqueous portion of the sap, and 



