352 PRINGIPLES OF Y E G E T 'a'tY^'K. 



laft ftage of exaltation, and be ripened into qualities perfeftly cpi^c-. 

 fponding to thoie of the tree. '■ '■"".' 



That plants partake of the nature of the foil whereon they grow is n(^o^ 

 riou^j and this .in no trifling degree: plants which in a free fo^l'^ay.^no 

 tiitfe'fn them, yet yield nitre when they growona nitrous foil, a^js often 

 experienced in the nitre- works in France. ' " '.' -^ - 



Xhough 1 "have faid plants may live by afTimilating fuch juices as they 

 V^« procure, yet* I apprehend if there be an abfolute dearth of fuc^ a? 

 are proper to them, though there be plenty of others in the fpot whq-p 

 they grow, they will pine, languifli, and die. fence water plants, can'r 

 not fupporta'dry foil^ and heath plants are rotted by^humidity. Never- 

 thelefs it is aflerted, that as the defert plains of Africa^ where a parched 

 and fandy foil prohibits vegetation, yield only mofles and lichens, fo the 

 higheft Alpine rcgioiis, and the mdft rigorous northern climates, yield 

 only mofies and lichens alfo. Strange, that the farne plants fhould fup- 

 port extreme's erf 'feat and cold, yel tefiife to ftourifh in temperate cli- 

 mates and richer {oris "l 



1 have heretofore confidered irritability as an indefinitely lower degree 

 6f.;fcnfi'bility i fof I confefs I am unable'to draw any line whereat to dif- 

 finguifh there principles. The irritability of plants is a curious fubjedi : 

 but not yet entirely elucidated. It is not always alike, but capable of 

 increpfe and decreafe ; is faid to bt greateft in the morning, lefs at noon, 

 fiill lefs in the everting; greateft in fpring, lefs in fummer, ftill lefs in 

 dutufnn : whether it be recruited by winter torpidity, therefore "moil 

 abundant in fprihg',, 6r by nightly repofe, therefore moft abundant in 

 themornirig ; or whether it may not depend on the different ftates of 

 the atmolphere, which inlpring and morning is humid and cool, is fub- 

 mitted. That humidity is grateful to plants is clear j that coolnefs cbn- 

 ftrids their fibres,' aS heat renders them flaccid, loofe, and therefore proba- 

 bly inert, by fealontofa'fnialler degree of tenfion, is alfo clear. Whether 

 this latter cauTe may not influence thofe plants which apparently follow the 

 fun has been doubted : for if thofe parts of the ftem whereon his rays 

 fall moft: immediately are thereby rendered weaker than thofe not ex- 

 pofed to his rays, doubtlefs they will give way, and the flower will bend 

 tbthat flde :' if this be granted, rhen, that coolnefs fliould cooftri(5l: the 

 fibres' of plants, that conftriflion Ihould adl principally on thofe parts 

 whieh had been expanded, /. <?. the flowers, is natural. That coolnefs ob- 

 tains befqrerai'n, and in the evening, is certain; and on this principle, 

 the cle^ftfre' of certain plants and flowers is thus accounted for: but as 

 -'^'^ fome 



