THE GENOTYPICAL RESPONSE OF THE PLANT 337 
‘be a difficult task to deny that these types are specialized to their re- 
spective regions. The influence of the habitat factors upon the com- 
position of the species-population is perhaps best illustrated in the 
case of Armeria vulgaris on the west-coast of Scandinavia. This coast 
strip runs through climatically widely different latitudes, and the popu- 
lation differs accordingly, as has been shown above. The northern- 
most type of the species is the var. sibirica Turcz. The succession of 
Armeria types on the Scandinavian coast-line partly repeats itself on 
the coast of Greenland, where the »maritima» type is confined to the 
southernmost portion of the coast, while the var. sibirica succeeds it to 
the north (KoLDERUP ROSENVINGE, 1896). 
2. THE CORRESPONDENCE BETWEEN THE ALTERNATION 
| OF HABITAT AND HABITAT TYPE. 
The controlling effect of environmental factors on the composition 
of a species-population is most clearly brought out in the cases where 
the reappearance of a distinct locality occasions the reappearance of 
the habitat type typical of that locality. The different H. umbellatum 
types furnish good evidence on this point. The alternation of sea-cliffs 
and shifting beach-dunes on the Swedish west-coast gives rise to a 
corresponding alternation of the bushy, broad-leaved sea-cliff type and 
the dune type. Wherever the H. umbellatum population on that coast 
strip has been investigated, the sea-cliff localities (Kristineberg, Mar- 
strand, Varberg, Hofs Hallar, Hallands Väderö, Kullen) have been 
found to harbour only the broad-leaved sea-cliff type. The beach dune 
localities investigated (Falkenberg, Halmstad, Torekov, Skelderviken, 
Nyhamn), which alternate with the cliff localities, have conversely been 
found to harbour the dune type. 
That a similar correspondence in the alternation of habitat and 
habitat type may take place within a geographically very limited area 
is seen from the distribution of the H. umbellatum types in the south- 
east corner of Scania. The successions of habitat types described be- 
low take place within an area found to be about 35 kilometres in ex- 
tent. The prostrate dune type of the arenacious fields is the only type 
found at Vitemölle, as was stated above. This type is succeeded by the 
Stenshuvud sea-cliff type south of Kivik, which again is replaced by 
the first-mentioned type a little farther to the south, where the sand- 
fields reappear. The type in question now flourishes as far south as 
the extent of the sandfield area, but is replaced by the type of the 
shifting dune as soon as the drift-sand of the Sandhammar region be- 
