GENERAL PROPERTIES OF GROWING PARTS OF PLANTS, 697 



The unknown factor which exists in the inherited properties of organisms is by 

 no means without analogy in inorganic nature. Chemists and physicists have also to 

 assume peculiar properties of elementary substances. The. aggregate of properties by 

 which a particle of iron is absolutely distinguished from a particle of oxygen is as 

 unknown and much more invariable than the aggregate of physiological causes which 

 distinguish the inherited properties of an oak from those of a pine. 



So far as the definition given above of historical properties concerns the 

 inherited specific peculiarities of plants, the term is not metaphorical from the 

 point of view of the Theory of Descent, but must be taken in its literal signi- 

 fication. The specific properties which determine qualitatively the growth of each 

 organ have sprung up successively in the course of time, i. e. in a series of genera- 

 tions. The chief evidence in favour of this view will be given in the last chapter of 

 this work. It need only be mentioned now that this theory of the genesis of specific 

 properties indicates the only possibility of arriving at an understanding of them 

 in accordance with the laws of causality. At the present time this is possible only 

 in the most general outline. 



The use here made of the terms 'historical' and 'physical' may also be illustrated 

 from another subject in the following manner. The nature of the geological form- 

 ations of which the crust of the earth consists can be understood only from a 

 historical point of view, because it is only at particular spots and at particular times 

 that the conditions have concurred which produced, for example, the Chalk or Old 

 Red Sandstone. The formation of these rocks was dependent on chemical and 

 physical processes, which must however have been preceded by other physical 

 changes in the crust of the earth, in order that these rocks should be formed exactly 

 at particular spots and particular periods. A crystal of sodium chloride can, on the 

 contrary, be produced at any time if the necessary conditions are artificially brought 

 together. Pseudomorphosis of crystals can again be explained only from a historical 

 point of view, although it is certain that the chemical and physical properties of the 

 substances are alone concerned in the process. We see therefore — and this is the 

 object of these remarks — that the historical explanation of a natural phenomenon 

 does not exclude its explanation from a physical point of view, but on the contrary 

 includes it where we have to do with natural phenomena ; and this principle is 

 equally applicable to those properties of vegetable species which have been acquired 

 hereditarily or historically, even when the application is practically much more diffi- 

 cult than in the case of inorganic nature. 



Sect. 13. General Properties of the G-rowing Parts of Plants \ From the 

 consideration of this subject the true crystals which are found in cells may be entirely 

 excluded, since they do not differ in their general properties from those which 

 occur elsewhere. The organised elementary structures on the contrary, the proto- 

 plasm, the nucleus, chlorophyll- and starch-grains, and the cell- walls, exhibit proper- 

 ties which distinguish them from all inorganic bodies. 



These organised bodies are, in the first place, all capable of swelling ; i. e. 

 they have the power of absorbing water or aqueous solutions between their solid 



* See Nageli u. Sclivvendener, Das Mikroskop, p. 403 et seq. 



