328 On the Anatomy of Vegetable*. 



parent, drier and firmer, it is becaufe it is continually ex- 

 pofed to the influence of the light and the air, and to the 

 contact of all thofe bodies which float in the atmofphere : 

 but it is not in reality a diftinct part; and it may be faid, 

 (triply fpcaking, that vegetables have no organ analogous 

 to the epidermis pf animals. When vegetables grow large, 

 the exterior membrane Teems to dilate ; but if this membrane 

 becomes extended, it is becaufe the number of the cells is 

 multiplied at the eircumference as at the exterior, and that 

 confequentlv the fides which compofe it are multiplied in 

 proportion, and increafe its capacity. 



One objection remains to be combated. It may here be 

 faid, Why is it fo eafy in the fpring time to detach the epi- 

 dermis from the young branches, ir it does not really form a 

 diftinct organ ? This may be explained in the following 

 manner : — All caufes which have an external action on the 

 vegetable alter its furface, and detach from it the interior 

 parts: but this feparation becomes more apparent when the 

 vegetation is more vigorous, and when the fluids moiften the 

 cellular tiiitie, and fill the tubes; for, as the diforganized 

 furface cannot then develop itfelf with the reft, it ceafes to 

 adhere, and often comes off in fragments, or is infenflbly 

 deftroyed. This is exactly what takes place in the fpring. 



In a word, this exterior ftratum, which fo many circum- 

 ftances tend to deftrcy, and which almoft always exhibits 

 traces of its disorganization, is not compofed of the laft 

 membrane onlv : the interior part of the cellular tiflue is 

 found in it, as is evident in the plane tree, and dill more in 

 the green oak, which produces cork. What has been here 

 faid is applicable only to the ftems and branches, which do 

 not die in the courfe of the year ; for in herbs, and the annual 

 parts of ligneous plants, fuch as the leaves, flowers, bracteae, 

 &c. the iurface does not detach itfelf from the reft of the 

 tiflue. 



But the epidermis of vegetables has no refemblance to that 

 of animals ; and, though it is certainly formed by the exte- 

 rior part of the cellular tiflue, it is no lefs true that its na- 

 ture is modified by fecondary caufes, and that it in fact be- 

 comes an organ, the functions of which are very diftinct, 

 and highly important. In the infancy of the vegetable, 

 when all the parts are foft and mucilaginous, it oppofes at 

 the fame time the difunion of the nafcent organs, and the 

 too ftrong action of the fluids. At a more advanced age, 

 when the juices are lefs abundant, it prevents their too fpeedy 

 evaporation, and maintains a juft equilibrium between the 

 folids and the fluids. At all times it fecures the vegetable 

 o from 



