THE SPECIES AND THE VARIETY AS ECOLOGICAL UNITS 101 
have been brought to light. KöLreuter (1761) showed that a species 
when pollinated simultaneously with its own pollen and pollen 
from another species breeds true to type in spite of the fact that it 
otherwise gives hybrids when crossed with that species. That the 
native pollen is favoured as compared with foreign has been shown 
by HERIBERT-NILSSON (1920) in the case of Oenothera Lamarckiana. 
He found that pollen tubes of O. gigas grew more slowly in the styles 
of ©. Lamarckiana than the O. Lamarckiana’s own pollen tubes. The 
terms elimination, certation, prohibition and substitution discussed by 
HERIBERT-NILSSON refer to phenomena which give rise to aberrant 
types of segregation. The importance of such gametic and zygotic 
complications has been discussed more recently by Nırssox-EuLE 
(1921). They are all particularly well calculated to throw light upon 
selective processes of great weight. However this »pre-natal selec- 
tion» may limit the output of new organisms, hybrids between already 
existing species would no doubt be more numerous and more widely 
distributed in nature were it not for the controlling effect of living 
and non-living factors of the outer world. Various disturbances in- 
volving different organs are frequently seen in hybrids and in »arti- 
ficial» species, and this fact does not support the idea that such or- 
ganisms are able to hold their own with nature. We are thus forced 
to the conclusion that the present-day species represent the only pos- 
sible and necessary outcome of the complex processes of selection in 
this epoch of the earth’s history (cp. HERIBERT-NiLsson, 1918). As a 
natural consequence we are led to the inference that a change in the 
inorganic world must bring about a corresponding change in the 
organic, inducing a recombination of Mendelian factors now distribu- 
ted in living organisms and resulting in the formation of new geno- 
type compounds or species (= evolution). 
The species problem is thus seen to be in a large measure an 
ecological problem. As such it has hitherto remained almost un- 
attacked from an experimental point of view. While at present the 
purely genetical side of the problem is fairly well understood, we have 
nothing like a reliable picture of the significance of the ecological 
factors in the differentiation process of the organisms. Our know- 
ledge with regard to the species problem may be shortly expressed 
by stating that while our understanding of the genospecies* is reaso- 
* The term genospecies is here meant to embody the known facts about the 
genotypical construction of the Linnean species; it has nothing to do with the 
genospecies of RAUNKIAER (1918), who employs the term in the sense of Lotsyan 
