Expla^nalion of the Cuticle of Leaves. 1G9 



ty»e forms of the haivs which contain the juices, will explain what 

 they are. I doubt not that most of the plants are much altered 

 from their first appearance when {^rowing in their original 

 mountains. Though I have taken all tlie plants I have dissected 

 from as appropriate situations as it was possible to procure them, 

 yet rock plants in particular must be very inferior in their cuti- 

 cles to what they would be could I have drav^'u them from their 

 native and original places ; most of the cactus and melon 

 thistles are of this kind ; they grow on the steep sides of rocks 

 in the hottest parts of America, where thev scetn to be thrust 

 out of the aperture, having scarcely a morsel of earth (and often 

 none at all) to assist them, though they are such large plants; 

 their roots shooting down into the fissures, and thus running to 

 a considerable depth, so that it is extremely difficult to procure 

 the plants. The roots appear to seek water onlv, for which their 

 little pumps serve them not alone for the purpose of clinging to 

 the rocks, but to moisten and invigorate the lower part of the 

 plants. 



It will be seen that though many of the vegetal)le tribe re- 

 ceive no nourishment from the atmosphere, vet they all have 

 the means of procuring the bark juices in their various different 

 ingredients. I before showed how many sorts of hairs each plant 

 possessed — long indeed before I had an idea that those separate 

 liquids, when collected and coagulated, formed the pabulum of 

 the leaf, and the bark juices. I may truly say that in this case 

 (as frequently before) nature has developed herself. I have 

 only had to show what appears in the microscope ; all the rest 

 arranges itself almost without my assistance, as too evident to 

 be misunderstood. I shall now close the present letter with the 

 account of the dissections that are intended to explain it ; and 

 in my next I shall conclude the subject v/ith the sand, fir, and 

 cryptogamia plants ; and with the variations each change of 

 soil, of moisture, or dryness, beyond their usual allotment, pro- 

 duces in the cuticle. 



'i^o give only a faint idea of how necessary all these matters 

 are to elucidate the knowledge of deeper philosophers, I shall 

 only mention, that all those curious trials established (1 think) 

 by Seniiebier, for want of it are useless ; saice the various ex- 

 periments he made to make plants grow in different matters 

 and soils were tried with plants that do not draw their nourish- 

 ment from tlie roots, but from the atmosphere: therefore most of 

 those that really succeeded may be supposed to have done so 

 because they touched not, nor interfered with, the soil bestowed 

 on them. It is so necessary in all these trials to understand 

 why we fail, and why we prosper. It is certain his attempt 

 could draw no result to be depended upon, and to be of real 



use 



