VARIATION. ADAPTATION. ORIGIN OF SPECIES 



385 



the greatest possible number of individuals, or, conversely, the greatest possible 

 differences between individuals. The first type of investigator tends to widen 

 the conception of species, the second to restrict it ; LINNAEUS' s species may be 

 taken as representative of the former, JORDAN'S of the latter. Looked at from 

 LINNAEUS'S point of view JORDAN'S species are to be regarded as 'petitesespeces,' 

 sub-species or as varieties, from JORDAN'S point of view LINNAEUS'S species are 

 to be considered as collections of species or sub-genera. According to the end 

 the author has in view the limits of the species will sometimes be wide, some- 

 times narrow. Obviously for our purpose the more restricted the limits of 

 species are the better, for if only their origin can be cleared up, the application 

 of the Theory of Descent to the origin of higher groups (sub-genera, genera, 

 families) presents no essential difficulty whatever. 



Let us take as an example the numerous forms of LINNAEUS'S species, 

 Draba (Erophila) verna, studied by JORDAN (1873), DE BARY and ROSEN (1889). 

 JORDAN distinguished more than 200 forms, each of which preserved its own 

 special characters for many generations with complete constancy. There can 

 be no doubt that more extended investigations would have resulted in the dis- 

 covery of an even greater number of 

 forms, distinguished by minuter differ- 

 ences, so that, in short, there would ap- 

 pear to be no limits to species-mongering. 

 How are the individual sub-species of 

 Erophila verna distinguished ? In ad- 

 dition to the general characters, which 

 are difficult to analyse, there are the 

 differential characteristics of form (con- 

 tour, margin) more especially of the 

 leaves of the radical rosette, the form 

 and number of the hairs, the appearance 

 of the floral leaves and the fruits. With- 

 out further description we may refer to 

 Fig. 113 from one of ROSEN'S illustra- 

 tions. 



It is very difficult in most cases to 

 attribute a use to a specific character, 

 and, again, it is just as difficult to furnish evidence that it can be of no service and 

 cannot arise in the struggle for existence. Still it must be admitted, as DARWIN'S 

 own investigations and later those of STAHL and HABERLANDT show, that many 

 characters previously believed to be of no service to the organism have distinct 

 functions and hence may have arisen by selection. It is always open to the 

 zealous Darwinian to assert that many a feature that is now of no import may 

 have been of service when it first appeared, for indifferent characters, if non- 

 injurious, may also be transmitted. But we have good grounds for taking 

 exception to the view that the species of Draba are all adapted forms which have 

 arisen in the struggle for existence. For instance, we very frequently find a 

 certain habitat of very limited extent occupied by several species forming an 

 association. It is highly improbable that each individual species arose as an 

 adaptation to a certain environment and then that these adapted types should 

 be collected together in a new habitat ; but even if this assumption be made, 

 it is very remarkable how three forms, let us say, a, b, c 9 which have originated 

 in three different places, each in complete harmony with its surroundings, should 

 collect in a new surrounding, and all be equally well adapted to the new conditions, 

 so that no one of them drives out the other. In addition to several species occur- 

 ring gregariously in one region, one and the same species occurs in quite different 

 habitats which have so little in common that they have been unable to affect 



Fig. 113. Erophila verna. After ROSEN (1889, 

 pi. 8). /, 'leaf rosette of Erophila spec. (/), of E. 

 graminifolia(2\ ofE. subtilis ( ?), of E. procerula (4\. 

 77, hairs of E. oblongata (i\ of E. procerula (2), of E. 

 graminea (j), of E. obconica (4). Ill, Flowers of 

 E. violacea (/). of E. subnitens (2), of E. scabra (j), 

 of E. majuscula (4). 



JOST 



c c 



