Explanalion of the Cuticle of Leaves. 163 



certified the changes tlius operated and caused in this jiart by 

 every alteration of soil and situation. It must here be observed, 

 that tiie extreme variation that has taken pLace in different plants, 

 from the desire now so vniversul of obtaining in every situation 

 and chmate ail the different species of flowers that can bv la- 

 bour and art be made to grow, and thus produce in one garden, 

 plants of all soils, of every climate, and every degree of mois- 

 ture, rock, sand, bog, water, herbaceous plants and trees : this 

 has so mixed the cuticles, that their habits are no longer to be 

 known by their outward appearance or form; indeed they by 

 degrees obtain new ones. 1 know few plants (except real water 

 plants and bog plants) that obstinately retain their customs, 

 and die if placed in an improper soil. The only means I have 

 been able to devise, to coviprehend this subject, and study it 

 completely, was to collect a few "of each different sort that still 

 j-etained their original properties unchanged by custom, and 

 make myself thoroughly accjuainted with their exact and natural 

 formation ; and when that was accomplished, to dissect those 

 which habit has altered. This I have done. A dozen plants of 

 each were sufficient to complete the task I had in view; and I 

 flatter myself I shall now be capable of discriminating clearly 

 the variations that take place, and give an exact account of 

 them. 



The leaves of trees and shrubs which are little indebted to the 

 atmosphere for support, consist of three upper cuticles and two 

 under ones ; I shall begin with the lowest part of the leaf: the' 

 under cuticle is a skin perfectly impervious to water, while the 

 next is a net which has on it bladders alternately placed in dia- 

 monds or otherwise; these rise high, and therefore keep the cu- 

 ticle hollow from tl>e pabulum of the leaf: these bladders are 

 very succulent, and cannot therefore bear the heat without being 

 destroyed and absorbed ; nor can the cuticle, hollow and dry as 

 it is, support the exposme.to the sun without being liable to 

 pqal oft, tear and break: hence the reason why, when once the 

 leaf is dried, it never again turns its back to the sun. Almost 

 every leaf is formed in the same manner in its under cuticle : next 

 to this skin comes the pabulum, vvliich is thick or thin according 

 as the leaf is so; for it is the increase of this part alone which 

 thickens a leaf. On each side of the pabulum the veins are to 

 be discovered : these contain the spiral wire : then follow the 

 three upper cuticles, the impervious one being in the middle : 

 (see Plate III. fig. 1.) Elm leaf dissected : when there are hairs, 

 they not only pass through the first skin, but pierce to the pa- 

 bulum, while the various divisions connect themselves with the 

 different vessels of the cuticle, see %. IX. This is admirably 

 seen by taking pains to adjust properly the compound micro- 



L2 



scope. 



