THE SPECIES AND THE VARIETY AS ECOLOGICAL UNITS 107 
edaphic factors are responsible for the splitting up of the ecospecies 
in these distinct varieties. The climatic differences would seem to be 
sufficiently great to produce a dissimilar development and differentia- 
tion of the population in the three localities. That the flora of the 
much exposed west coast of Sweden is very different in character 
from the flora of the more sheltered, less extreme eastern coast is 
well known. I have pointed out in a previous publication (TURESSON, 
1919) that numerous prostrate plant forms are found on the exposed 
west coast. This is especially true of the species belonging to the 
genus Atriplex, and therefore it is not surprising to find that the west 
coast variety of the Atriplex ecospecies under discussion differs from 
the eastern representative precisely in regard to stature. Forms with 
hereditary erect branches are rare in the west coast variety. That 
prostrate forms of the species are »favoured» on the west coast, while 
erect ones tend to become eliminated, seems then to be a very reaso- 
nable assumption. 
The experience gained from other species in the course of these 
studies considerably strengthens the assumption of the importance of 
climatic and edaphic factors in the differentiation process of varieties. 
Some examples are here given. The coast form of the common scent- 
less camomile, Matricaria inodora var. maritima, occurs both on the 
west coast and on the east coast. The coast form differs from the 
inland forms in many characteristics but especially in having thick, 
fleshy leaves and bushy growth, both these features being hereditary 
and constant in cultures. When sets of individuals of this coast form 
collected in various places (where hybridization with the inland form 
is excluded) along the east and west coasts are studied comparatively 
in cultures, important differences between the eastern and western 
sets will at-once be seen. The west coast sets always contain more 
numerous prostrate types than the east coast sets, and the fleshiness 
of the leaves is much more pronounced throughout in the former than 
in the latter. Collections of other plant species show similar peculiari- 
ties. Mention may be made of Solanum dulcamara, a plant with an 
extensive distribution in Sweden. Sets of this plant from different 
points on the east and west coasts have been cultivated and studied 
comparatively. It is found that the eastern sets contain all kinds of 
types as to characters of leaf, while sets collected on the exposed 
western coast show a remarkable conformity in type being all re- 
ferable to the hairy, thick-leaved form called S. dulcamara f. ma- 
rinum, Bas. 
