NATURAL HISTORY. 



S25 



fluids, and that a constant supply 

 is necessary, without which they 

 soon perisli. This supply, so ne- 

 cessary, must be taken in by ab- 

 sorption : and it is this act of ab- 

 sorption that I shall endeavour to 

 prove to be the efficient cause of 

 these motions in vegetables, and 

 thus exclude volition from having 

 any causation in these phenomena ; 

 for it is'froni their not haviucr been 

 explained upon mechanical princi- 

 ples, that mind has been resorted 

 to. Mind is in general our last re- 

 source, when wc fail in explaining 

 natural phenomena. I could wish 

 that phvsiologists were agreed upon 

 the kind of absorption which takes 

 place here, wliether it be by active 

 open-mouthed vessels, which in the 

 common opinion takes place in the 

 animal economy, or by capillary at- 

 traction, which is the most general 

 opinion in the vegetable j but the 

 theory I shall offer to the consider- 

 ation of the Linnean Society will 

 agree with either. 



The first consideration is — That 

 an inert fluid is in motion. 



Secondly — That, possessing no 

 motion in itself, it owes this motion 

 to the plant. 



Tliirdly — That as action and re- 

 action are equal, whilst the plant 

 draws the fluid towards itself, it 

 must be drawn towards the fluid, 

 and that in the reverse ratios of 

 their respective resistances. 



Now whether this absorption be 

 performed by vessels acting as in 

 the animal economy, or by vessels 

 of the nature of capillary tubes, is 

 of little moment, provided only that 

 an absorption be admitted ; for it 

 is evident, that if action and re- 

 action be the same, the absorbed 

 fluids, which possess no motion in 



themselves, cannot be put in mo- 

 tion by the open-mouthed active 

 vessels, without being drawn in the 

 direction of the absorbed fluids. — 

 But sliould we prefer the theory 

 wliich explains this absorption by 

 capillary attraction, which theory 

 I think is the most prevalent, we 

 shall still find that the absorbing 

 vessels are drawn towards the fluid. 

 Tills is equally true as evident, 

 whether applied to that simple 

 hydrar.lic instrument, the straw, 

 through which the school-boy sucks, 

 or to the most complicated ma- 

 chine of the natural philosopher. — 

 Tliese principles will, I think, be 

 sufficient to explain those appear- 

 ances in vegetables wliich have 

 served as a foundation, or have 

 been considered as signs of their 

 perceptivity and volition, and which, 

 as far as I have learnt, have never 

 been attempted to be explained, 

 viz. the direction of their roots to- 

 wards the soil which aff'ords them 

 the best nourishment, and the young 

 and tender shoots towards the light : 

 for here is an absorption of water 

 and light. The absorption of water 

 is easily ascertained ; but that of 

 light, by its subtlcnesi;, eludes our 

 experiments, with probably many 

 other fluids of great importance to 

 the healthy state of the vegetable 

 world. But to make the connexion 

 more complete between the two 

 organic kinp'doms, it has not only 

 been found that plants move to- 

 wards their food like wise and intel- 

 ligent being*;, but they likewise 

 turn aside from tliose soils, &c, 

 which are injurious to them, or at 

 least afford them but a scanty 

 nourishment. This is a deception : 

 it is only the immediate conse- 

 quence of their motion towards 

 Y .'3 their 



