100 On the /inalomy of Vegetables ; inlended to .mh^lantlalc 



il. That the roots and leaves of a plan: will most exactly 

 mark not only what is the soil in which they originally grew, 

 but the situation from which they came, whether a ivater plant 

 or a dry plant, a rock or a valley plant, &c. 



12. That the water, and semi-water, and rock ))lants alone 

 can be said to have direct air-vessels, though 1 have found them 

 in j)arasite and early spring plants, such as tlie crocus and hya- 

 cinth. 



13. That the leaf owes all its mechanism to the gatherer 

 alone. 



When I have shown the absolute trutli of all tliese proposi- 

 tions in a way, I liope, that caimot v/cU be contradicted, I have 

 many more with which constant dissection has accjuainted me, 

 which will allogct/icr (I flatter mvself) exhibit a regJilar 

 system formed by Nature, and established in trutli; which may 

 at last force conviction even on those learned botanists, who 

 have such a holy horror of committing themselves, that they dare 

 not trust their superior minds to hold the scale between truth 

 and falsehood, and try the argument by a fair examination, and 

 by the complete consistencv of the opinions. 



My first proposition is," That there is no perspiration in plants." 

 I have already said much on this subject. I shall now therefore 

 only recapitulate the simple facts, and the manner in which I 

 prove that there is none. I shall first show the difference be- 

 tweeen perspiration and evaporation, since to comprehend terms 

 clearly, elucidates a subject beyond any other means. Perspira- 

 tion is a matter thrown off in its liquid state, from apertures 

 contrived for the purpose, being a matter injurious to health, 

 and therefore necessaiy to be rej)elled : it is often seen in drops 

 of water on the skin. But evaporation is merely a sign that water 

 exists there. It flies off in vapoiir unseen; and whether it is or is 

 not condensed again, depends on the presence or absence of one 

 of its constituents, hydrogen, which, the moment it appears, has 

 such an affinity for oxygen that they directly join and recompose 

 water. Novv the chief proof which Hales gives of the persi)iration 

 of plants is, that if you place a vegeta])Ie in a bell-glass, drops of 

 water will soon run down the interior suri'ace. This is true ; but 

 is easily e;<[)!ained. Oxygen flows in (quantities from every healthy 

 plant: it is taken from the decomposed water in the vegetable, 

 and the hydrogen is secreted. But when a plant is oppressed 

 and sick, it parts with this gas ; and this is shown by the damp 

 clammy feel it acquires. As soon therelbre as confined under a 

 glass without free air, it begins to lose its hydrogen; which im- 

 mediately flying to the oxygen it had before given out and con- 

 fined, they again combiivj and form water. But turn a strong 

 magnifiei- on the plant uhilc under the glass, and not one drop 



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