140 
FURTHER OBSERVATIONS 
It is eafy to flop a gentle ouzing from an old wound of a 
Vine, by applying foft clay, putty, or warm wax to the 
wounded part : I have, however, fometimes found, that foot, 
or 
“ ftrufted in the fame manner. Sallows, willows, Vines, and moft fhrubs 
“ will grow in an inverted ftate, v/ith their tops downward in the ^earth. 
“ Dr. Bradley defcribes the manner of inverting a young cherry-tree, the 
“ roots of which will put forth leaves, and the branches become roots. Hence 
“ it is obvious, that the nutritive matter may be conveyed as well by the leaves 
“ as the roots, their vafcular ftrudlure being the very fame. 
“ During the heat of a fummer’s day, all plants perfpire freely from the pores of 
“ their leaves and bark. At that time the juices are highly rarefied 5 and the 
“ diameters of the Tracheae, or air-velTels, are enlarged fo as to prefs upon 
“ and ftra'iten the veflels that carry the fap. In confequence of which, tlrcir 
“juices, not being able to efcape by the roots, are prefled upw'ard, where 
“ there is the leafl; refiflance, and perfpire oft’ the excrementitious parts by the 
“ leaves and top-branches in the form of vapour. When the folar heat de- 
“ dines, the Trachea; are confaded. The fap-veflels are enlarged, and the 
“ fap finks down in the manner of the fpirits in a thermometer. In confe- 
“ quence of this change, the capillary veflels of the leaves and top-branches 
“ become empty. Being furrounded with the humid vapours of the evening, 
“ they fill themfelves from the known laws of attradion, and fend down the 
“ new-acquired juices to be mixed with thofe that are more elaborated. 
“ As foon as the fun has altered the temperature of the air, the Tracheae be- 
“ come again diftended, and the fap-velTels are llraitened. The fame caufe 
“ always produces the fame effed ; and this alternate afcent and defcent, 
“ through the fame fyflem of vefTels, continues as long as the plant furvives. 
“ The irregular motion of the ftem and branches is another caufe that contri- 
“ butes to the afcent of die fap. Every time that thefe parts are aded upon 
“ by the air, they are made to alTume a variety of angles, whereby the fap- 
“ veflels 
