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. Jt 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’, 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”; 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 
* 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.” 
? Compare Kohl’s work on Anatomisch-phys. Untersuchungen iber Kalksalze, etc. 
Marburg, 1889, 
15—2 
