THE GENOTYPICAL RESPONSE OF THE PLANT 347 
blem. The importance of this line of research for the understanding 
of bio-geographical and bio-sociological questions is also evident. 
SUMMARY. 
Material of a number of Linnean species, brought under culture, 
has revealed the presence of a considerable hereditary variation 
within each species. 
The hereditary variations of the species have been found in nature 
to be grouped into different types confined to definite habitats. Cer- 
tain characteristics have been found to be common to all or to 
the majority of the individuals of each type, while other charac- 
teristics vary. 
The following facts bring out particularly well the intimate relation 
of these habitat types to the habitat factors: 
a) The characteristics of the types are apparently such that they 
specialize the types for certain habitats. 
b) With regard to Hieracium umbellatum a close correspondence 
is found between the alternation of habitat and habitat type. 
c) Cases have been found where a local differentiation of the ha- 
bitat type from the species-population has in all probability 
taken place. 
d) There is a morphological parallelism between the modification 
and the hereditary variation. 
The evidence at hand does not support the idea that the habitat 
types have originated through sporadic variations preserved by 
chance isolation. On the contrary. the facts go to show that the 
habitat type represents the genotypical response of the species- 
population to a definite habitat. 
The Linnean species represents an ecological unit of great im- 
portance. It is specified as a coenospecies (defined above), nar- 
rowed down to the ecological combination-limit. A genotype com- 
pound of this order is here termed an ecospecies. 
The term ecotype is used as an ecological sub-unit to cover the 
product arising as a result of the genotypical response of an eco- 
species to a particular habitat. 
The term ecophene is proposed to cover each of the reaction-types 
of the ecotypes arising through the modificatory influences of the 
combinations of extreme habitat factors given in nature. 
