Specific Structure 227 



fertilisation. In dioecious plants we must aim at the reproduction of 

 brothers and sisters. 



We may at the outset take it for granted that a pure species 

 remains the same under similar external conditions; it varies as 

 these vary. It is characteristic of a species that it always exhibits 

 a constant relation to a particular environment. In the case of two 

 different species, e.g. the hay and anthrax bacilli or two varieties of 

 Campanula with blue and white flowers respectively, a similar environ- 

 ment produces a constant difference. The cause of this is a mystery. 



According to the modern standpoint, the living cell is a complex 

 chemico-physical system which is regarded as a dynamical system of 

 equilibrium, a conception suggested by Herbert Spencer and which 

 has acquired a constantly increasing importance in the light of 

 modern developments in physical chemistry. The various chemical 

 compounds, proteids, carbohydrates, fats, the whole series of different 

 ferments, etc. occur in the cell in a definite physical arrangement. 

 The two systems of two species must as a matter of fact possess a 

 constant difference, which it is necessary to define by a special term. 

 We say, therefore, that the specific structure is different. 



By way of illustrating this provisionally, we may assume that 

 the proteids of the two species possess a constant chemical difference. 

 This conception of specific structure is specially important in its 

 bearing on a further treatment of the subject. In the original cell, 

 eventually also in every cell of a plant, the characters which after- 

 wards become apparent must exist somewhere ; they are integral 

 parts of the capabilities or potentialities of specific structure. Thus 

 not only the characters which are exhibited under ordinary conditions 

 in nature, but also many others which become apparent only under 

 special conditions 1 , are to be included as such potentialities in cells; 

 the conception of specific structure includes the whole of the poten- 

 tialities of a species ; specific structure comprises that which we 

 must always assume without being able to explain it. 



A relatively simple substance, such as oxalate of lime, is known 

 under a great number of different crystalline forms belonging to 

 different systems 2 ; these may occur as single crystals, concretions or 

 as concentric sphaerites. The power to assume this variety of form 

 is in some way inherent in the molecular structure, though we cannot, 

 even in this case, explain the necessary connection between structure 



1 In this connection I leave out of account, as before, the idea of material carriers of 

 heredity which since the publication of Darwin's Pangenesis hypothesis has been frequently 

 suggested. See my remarks in " Variationen der Bliiten," Pringsheim's Jahrb. Wiss. Bot. 

 1905, p. 298; also Detto, Biol. Centralbl. 1907, p. 81, "Die Erklarbarkeit der Ontogenese 

 durch materielle Anlagen." 



2 Compare Kohl's work on Anatomisch-phys. Untemichungen ilber Kalktalze, etc. 

 Marburg, 1889. 



15—2 



