60
M. E. D. P O O R E
Carex saxatilis sociation found by Poore in Central Scotland (Poore.
195513) with the Scandinavian sociation for Sylene in Central Norway
(Nordhagen, 1928). It seems very probable that these are local segregates of a post-glacial sociation from which the present representatives
have originated by subsequent divergent migration.
Fossil evidence supports the occurrence of such migration of the
plant community as a structural unit. Table I1 is taken from Cain (1944)
and compares the common list of trees from the modern forest at Jasper
Ridge, Palo Alto, California, and the matching species of the Miocene
Mascall Flora (Chaney, 1925).
T A B L E I1
A Comparison of the Common Trees of the Modern Forest
at Jasper Ridge, Pal0 Alto, California, and the Matching Species
of the Miocene Mascall Flora
Jasper Ridge Flora
Mascall Floru
Sequoia sentpervirens
Sulix laevigata
Snlix bsiolepis
Populwr trichocurpa
dlnwr rhombifolia
Quercwr Kelloggii
Quercus agrifolia
Quercwr lobata
Umbellularia califwrtica
Arbutus Menziesii
Acer nzaerophyllum
Aesculua ealifornica
Sequoia langsdorji f i i
Salix varians
Salix varians
Popuha lindyretti
Abius sp.
Quercus pseudo-lyratir
Quercua convexa
Quercua duriusculo
Umbellularia sp.
Arbutwr sp.
Acer bolanderi
Absent
From Cain, 1944
I n the course of time communities migrate in response t o secular
changes of climate; and they change as they migrate. The evolution of
new species contributes to this change, but it is also brought about by the
break up and extinction of parts of the community and by segregation
or recombination of its elements.
Evidence is found in the post-glacial history of British vegetation of
the segregation of grassland and ruderal communities from species
which occupied a rare and sporadic place in the intervening woodland
phase (Godwin, 1956).
In a discussion of Leskov's work on an Abies forest Sukachev (1044)
shows how in his view Pinus forests have not differentiated out of one
primitive stock but have arisen though the Pine colonizing and conibining with other and different floristic elements. This does not only
M. E. D. P O O R E
Carex saxatilis sociation found by Poore in Central Scotland (Poore.
195513) with the Scandinavian sociation for Sylene in Central Norway
(Nordhagen, 1928). It seems very probable that these are local segregates of a post-glacial sociation from which the present representatives
have originated by subsequent divergent migration.
Fossil evidence supports the occurrence of such migration of the
plant community as a structural unit. Table I1 is taken from Cain (1944)
and compares the common list of trees from the modern forest at Jasper
Ridge, Palo Alto, California, and the matching species of the Miocene
Mascall Flora (Chaney, 1925).
T A B L E I1
A Comparison of the Common Trees of the Modern Forest
at Jasper Ridge, Pal0 Alto, California, and the Matching Species
of the Miocene Mascall Flora
Jasper Ridge Flora
Mascall Floru
Sequoia sentpervirens
Sulix laevigata
Snlix bsiolepis
Populwr trichocurpa
dlnwr rhombifolia
Quercwr Kelloggii
Quercus agrifolia
Quercwr lobata
Umbellularia califwrtica
Arbutus Menziesii
Acer nzaerophyllum
Aesculua ealifornica
Sequoia langsdorji f i i
Salix varians
Salix varians
Popuha lindyretti
Abius sp.
Quercus pseudo-lyratir
Quercua convexa
Quercua duriusculo
Umbellularia sp.
Arbutwr sp.
Acer bolanderi
Absent
From Cain, 1944
I n the course of time communities migrate in response t o secular
changes of climate; and they change as they migrate. The evolution of
new species contributes to this change, but it is also brought about by the
break up and extinction of parts of the community and by segregation
or recombination of its elements.
Evidence is found in the post-glacial history of British vegetation of
the segregation of grassland and ruderal communities from species
which occupied a rare and sporadic place in the intervening woodland
phase (Godwin, 1956).
In a discussion of Leskov's work on an Abies forest Sukachev (1044)
shows how in his view Pinus forests have not differentiated out of one
primitive stock but have arisen though the Pine colonizing and conibining with other and different floristic elements. This does not only