iO On the Nourishment produced to the Plant hj its Leaves. 



fact respecting the putridity of one part of a vegetable, well 

 worth the attention of v. good chemist. When a plant is gathered 

 or cut down, the line of life rarely lives a few hours, but the 

 gatherer of the leaf grows black sooner, and even precedef, it in 

 decomposition. Behold that of the French bean, or pliascoliis vvl- 

 oaris ; the acacia ; plane tree : indeed any leaf whose gatherer 

 is large enough to show it well, and it will be found to begin its 

 decomposition almost within the hour. 1 used to fancy it was 

 the quantity of oil taken in by the hairs to lubricate tlie spiral 

 wire ; but it has so much resemblance to the general dfcay of 

 the water plant, that I think I must be mistaken; a fresh-water 

 plant soon decays in salt water, and a sea-weed scon decom- 

 poses in fresh water. We know that a fish carries down a large 

 bladder of air to support it, and so does the fresh-water plant ; 

 but there must be some very ciu'ious reason for its decomposing 

 po cjuirkly. I have read (but I cannot recollect my author) 

 that the fresh-water plants at the side of the rivers in Africa lie 

 down like the sea-iveed, and recover again when the rainy sea- 

 son restores the waters: 1 think it must be a mistake, for then 

 they must be wholly free from all interior vessels, as are the salt- 

 water plants. 



I shall now endeavour to show the curious changes produced 

 on the cuticle of leaves, by the excess of hiimidily or dryness. 

 When a semi-water plant loses the rill or ditch that snstaint-.d its 

 moisture, I have' before shown that its air-vessels by degrees 

 contract till they scarce deserve the name, gaining also addi- 

 tional quantities of hairs on tlieir leaves, to make them some 

 little amends for the moisture their root used to dispense. Thus 

 they continue to grow like land plants, as long as the ditch re- 

 mains dry that used to feed them. 



Viewing a ([uantity oi circcea bisilanica, I observed that those 

 which grew in or near the stream had (as usual) their stems and 

 leaves full of air vessels, and that they were almost wholly free 

 from hairs ; but on examining some higher up the bank, they 

 were not only entirely free from air-vessels but had also quanti- 

 ties of hairs to supply them with water, and at the summit of the 

 bank their upper cuticle was crippled with points. Now this is 

 a sort of succedaneum I have so frequently discovered, when 

 dissectiuL^ plants, that 1 believe it is the common resource of 

 nature either in very dry or vert/ wet weather. I have often 

 on these occasions (wiien wet weather has long prevailed) taken 

 up roots, and found them (especially in herbaceous plants) partly 

 covered at the exterior with a thin layer of air vessels, as if to 

 protect them from the too great humidity of the ground ; and 

 when, on the contrary, nature has been oppressed with a super- 

 abundance of dry weather, I have found the roots equally covered 



with 



