342 GOTE TURESSON 
as is done by these writers, is largely to strip the ordinary species, as 
found in nature, of one of its most characteristic qualities, viz. the 
ability to respond genotypically to a wide range of different habitats 
with such units or habitat types, representing various combinations 
of Mendelian factors. The further discussion of this subject leads 
to a consideration of the species and the variety as ecological 
units. . ; 
The concept of the species has undergone various changes since 
the time of Linnageus, Darwinism, as also Lamarckism before it, 
by the nature of the theory led to the conception of the species as 
mere conventions, set up in order to facilitate a classification of ever- 
changing and therefore not clearly defined groups. The genetical ana- 
lyses of Linnean species have again brought about a change; the geno- 
type has now become the real unit, while the »collective» species is 
still to a large extent considered a conventional conception. This ge- 
neral notion is also reflected in the species-concepts recently pro- 
pounded (Lorsy, 1916; HaGepoorn, 1921). Whether this is a legi- 
timate procedure, or whether it does not at the same time reflect 
the failure on the part of these investigators rigthly to appreciate 
the ecological side of the species problem may perhaps be gathered 
from the following. It is well known that during the last two decades : 
great progress has been made with regard to the experimental study, 
of the species problem from the genetical point of view. Not only 
has Mendelism gone far to show that species follow the same laws 
as varieties with regard to segregation and combination; it has also 
been able to demonstrate and to a certain extent copy Nature’s own 
course in the building up of new species. This has been admirably 
shown by Lorsy (1916) in the well known case of Antirrhinum 
rhinanthoides, produced from a cross between A. giutinosum and A. 
majus and so different from its parents that a trained botanist would 
refer it rather to the genus Rhinanthus than to Antirrhinum. It is 
constant in certain characters but varies in other in the same wayias 
the Linnean species. The extravagant types produced by HERIBERT- 
Nırsson (1918) from various Salix crosses belong to the same category 
of facts. All of them (Salix amerinoides, S. pendulifolia, S. monandra) 
demonstrate in a striking way the process by: which new and morpho: 
logically very remarkable organisms arise. 
Thus, while the belief that the Limnean species of the present 
genetically represent complicated products of recombined Mendelian . 
factors, or genotype compounds, has been strengthened, few would 
