162 Explaiiation of the Cuticle fif Leaves. 



wg to it, the stroke of death has not yet attained it. I have 

 shown the amazing variety of juices received by the hairs and 

 cuticles from the atmosphere. Now those who have ever de- 

 composed the bark Hquid know that it is formed of many dif- 

 ferent sorts of matter. It is very probable, then, among 

 the variety of licjuids absorbed by the hairs and cuticles, that 

 gluten, gelatine, tannin, &c. all enter the plant in separate juices, 

 and are received by those parts, nor unite to form the compound 

 till they meet and compose the pabulum of the leaf, and after- 

 wards its superabundance settles in the bark, and fills the inner 

 bark vessels. All plants that die partly down in the winter lose 

 their bark juices, nor regain them till after the leaves are 

 formed : the vine, for examjde, the lavender, and innumerable 

 other plants. But if the bark juices are thus formed, they be- 

 gin to collect in the leaf- bud the preceding autumn ; when within 

 the gemma they retain a quantity of these juices ready prepared, 

 and in an almost coagulated state for the shooting of the leaf- 

 vessels. I cannot but l>e persuaded that this is tlie real origin 

 of the blood of the ]jlant, for in the root we most easily trace 

 the sap proceeding from the earth. But no power that 1 could 

 exert, no dissection that I could contrive, has been able to show 

 me any other origin of the bark juices: they flow not from the 

 earth, nor are they formed in the root ; but from the Laves I have 

 ever discovered much probabUify of tlieir proceeding. All plants 

 with respect to the different formation of their cuticles may be 

 divided into eight sorts. Trees and shrubs receive but little 

 nourishment from the atmosphere, their roots alone aftording 

 them plenty. Evergreens absorb none at all. Herbaceous and 

 annuals gain a vast deal of supjwrt from the rains and dews. 

 Bog plants hardly any in this way, and are therefore more hurt 

 by a change of situation than any other except downright water 

 plants ; because they can in their leaves receive no indemnifica- 

 tion for the loss of food to their roots. .Sand plants receive 

 much of their support from the atmosphere ; while rock plants 

 are wholly fed by its means, and draw no assistance from any 

 other source : the leaves of firs are incapable of receiving mois- 

 ture J the cuticles being too much like evergreens, and too well 

 guarded to admit it ; and as to water plants, 1 have already 

 shown tlieir general furmation in my last letter. There is how- 

 ever much that concerns their outward skin, which will admit 

 of some detail, and which I shall give in my next. No property 

 of nature is more wonderiul than that which vegetables possess, 

 of adapting the cuticles of their leaves to the different situa- 

 tions in which they find themselves placed. This is so peculiarly 

 the case, that I could scarpely credit the evidence of my eyes, which 



certified 



