NATURAL HISTORY. 



S27 



"winds, or other agents, capillary at- 

 traction, and, probably, something 

 in the conformation of the vessels 

 ihemsclves, which renders them 

 better calculated to carry iliiids in 

 one direction than in another. 1 

 shall begin with a few observations 

 on the leaf, from whrch all the de- 

 scending fluids in the tree appear to 

 be derived. This organ has much 

 engaged the atteriiioa of naturalists, 

 particularly of Ai. Bonnet, but their 

 experiments havt}. chiefly been made 

 on leaves severed from tiie tree ; 

 and, therefore, whatever conclu- 

 sions have been drawn, stand on 

 very questionable ground. 'I'he ef- 

 forts which plants always make to 

 turn the upper surfaces of their 

 leaves to the light, have with reiison 

 induced naturalists to conclude, that 

 each surface has a total distinct of- 

 fice ; and the following experiments 

 tend strongly to support that con- 

 •ch!^io^. 



I placed a small piece of plate 

 glass under a large vine leaf, with 

 its surface nearly parallel with that 

 of the leaf, and as soon as the glass 

 had acquired the temperature of the 

 house in which the vine grew, I 

 brought the under surface of the 

 leaf into contact with it, by means 

 of a silk threaxl and a small wire, 

 adapted to its form and size. Hav- 

 ing retained the leaf in this po.^ition 

 one minute, I removed it, and found 

 the surface of the glass covered with 

 .1 strong dew, which had evidently 

 <;xhalcd from the leaf. 1 again 

 brought the leaf into contact with 

 the glass, and, at the end of half an 

 hour, found so much water dis- 

 charged from the leaf, that it ran 

 oft" the ghiss when held obliquely. 

 1 then inverted (he position of the 

 leaf, and placed its upper surface in 

 lOHtact VNitb tlie glass: not the 



slightest portion of moisture now 

 appeared, though the leaf was ex- 

 posed to the full inllucnce of the 

 meridian sun. These experiments 

 were repeated on many different 

 leaves, and the result was in every 

 instance precisely the same. It 

 seems, therefore, that in the vino 

 the perspiratory vessels are confined 

 to the under surface of the leaf; 

 and these, like the cutaneous lym- 

 phatics of the animal economy, are 

 probably capable of absorbing mois- 

 ture, when the plant is in a state to 

 require it. The upper surface 

 seems, from the position it always 

 assumes, either formed to absorb 

 light, or to operate by tlie influence 

 of that body ; and, if any thing ex- 

 hale from it, it is probably vital air, 

 or some otlier permanently elastic 

 lluid. It nevertheless appears evi- 

 dent in the experiments of Bonnet, 

 that this surface of the leaves of 

 many, when detached from the tree, 

 readily absorbs moisture. 



Selecting two young shoots of 

 the vine, growing perpendicularly 

 against the back wall of my vinery, 

 I bent them downwards, nearly in a 

 perpendicular line, and introduced 

 their succulent ends, as layers, into 

 two pots, without wounding the 

 stems, or depriving them of anj 

 portion of their Icavt^s. In this po- 

 sition the shoots, which were about 

 four feci long, and sprang out ot the 

 principal stem about three feet from 

 the griiund, grew freely, and in the 

 course of the summer reached the 

 top of the house. As soon as their 

 wood became sulViciently solid to 

 allow nie to perform tht; operation 

 with safety, 1 made two circular in- 

 cisions through the bark of the 

 depemling part of each shoot, at a 

 small dislance from (^ach oilier, near 

 the Kurfcice of the mould in the pote; 



and 



