228 THE FORMATION 
with indigenous and autochthonous, while others have regarded it as an 
antonym of exotic. In its proper sense, endemic refers to distribution, and 
not to origin. Its exact opposite will be found then in Fenzl’s term poly- 
demic, dwelling in several regions. Indigenous (autochthonous) and exotic, 
on the contrary, denote origin, and are antonyms, indigenous signifying 
native, and exotic foreign. As Drude has shown, endemic plants may be 
either indigenous, as in the case of those species that have never moved out 
of the original habitat, or exotic, as in the much rarer instances where a 
polydemic species has disappeared from its original home and from all 
regions into which it has migrated except one. It is understood that not 
all indigenous or exotic species are endemic. The proportion of endemic to 
polydemic species is a variable and somewhat artificial one, depending upon 
the size of the divisions employed. . 
277. Causes. The primary causes of endemism are two, lack of migra- 
tion and presence of barriers. Since distributive agents are practically 
universal, lack of migration corresponds essentially to immobility, a fact 
which decreases the difficulty of ascertaining the immediate causes of 
endemism in any particular species. Either immobility or a ‘barrier may 
produce endemism; extremely immobile plants, for example, liliaceous 
species propagating almost whollv by underground parts, are as a rule 
endemic, while alpine plants and those of oceanic islands are endemic in 
the highest degree, regardless of their mobility. When the two conditions 
act concomitantly upon a species, endemism is almost inevitable. It can not 
be supposed, however, that immobility or natural barriers alone, or the 
concomitance of the two, must invariably give rise to endemic species; the 
most immobile plant may be carried into another region by unusual or 
accidental agencies, or the most formidable barrier to migration may be 
overcome by the intensity of an agent or through the action of man. En- 
demism is also brought about by the modification of species; new or 
nascent species are as a rule endemic. Whether they will remain endemic 
or not will depend upon the perfection of their contrivances for dissemina- 
tion and upon the presence of harriers to migration or ecesis, Finally, as 
Drude was the first to point out, the disappearance of a polydemic species in 
all regions but one, owing to the struggle for existence or to changed 
physical conditions, will result in endemism. 
278. Significance. Endemjsm is readily recognized by methods of 
distributional statistics, applied to areas limited by natural barriers to 
migration or ecesis. For political areas, it has no significance whatever, 
unless the boundaries of these coincide with barriers. It determines in the 
