340 



to suppose that living matter is capable of moulding, as it 

 Aveve by one operation, inorganic matter, suitable, perhaps, 

 as to ultimate composition, but of the most diverse proximate 

 arrangement into molecular aggregation like its own. It is 

 inconceivable that any given stage of evolution can be reached 

 with equal facility from any inferior stage selected at hap- 

 hazard. 



Compare what takes place in plant nutrition. Under the 

 influence of solar light the inorganic materials appropriated 

 by the tissues of plants undergo successive modifications, 

 which, weakening the stability of their molecular constitu- 

 tioUj "give collateral affinities the power to work a rearrange- 

 ment, which, though less stable under other conditions, is 

 more stable in the presence of these particular undulations."' 

 But an essential element in these changes is their occurrence 

 in connection with the colloidal materials of vegetable tissues 

 which bring the carbon dioxide, ammonia, and water, on 

 which the rearrangement is effected in a condensed state into 

 close contiguity. As soon as the bonds which unite their 

 component elements are Aveakened by the unequal effect of 

 the undulations propagated by solar light on their unequal 

 atomic activities, they are ready to enter into new and inter- 

 changed combinations. In this way, by mutual actions and 

 reactions, substances independently more unstable are elabo- 

 rated from the more stable, and these being more and more 

 like the materials in the presence of Avhich the changes are 

 effected, tend finally to be integrated with them, every stage 

 in the process being a position of equilibrium between the 

 molecular constitution and environing influences. By pro- 

 cesses of which this is a rough outline, the conversion of 

 inorganic into living matter is effected ; but the presence of 

 pre-existing living matter is a very potent factor in the change. 

 It brings the component materials together, effects their joint 

 exposure to solar influence, shapes the final form of their 

 combinations, and gives them a stability they could not 

 possess apart from it. Probably the merely physical and col- 

 loidal properties of the living matter in conjunction with solar 

 action effect the union of the ultimate into proximate con- 

 stituents, and then the " coercive polar force" of the com- 

 ponent molecules of the living matter cause them to aggregate 

 into similar molecules. There is plenty of analogy to induce 

 a belief in such a coercive influence of an aggregate on in- 

 tegrable units ; a broken crystal, for example, tends first to 

 restore its shape before receiving further additions.^ In this 



' ' Principles of Biology,' vol. i, p. 32. 



" Another good illusM-ation of the tendency of similar molecules to 



