Plants of the Northern Temperate Zone in their 
Transition to the High Mountains of Tropical 
Africa. 
BY 
A. ENGLER. 
I N building up the theories of the evolution of species, those plants which 
are either fully identical or appear as closely allied forms in widely 
separated localities, have always received special attention. It is known 
that it is not unusual to find one and the same species or nearly related 
ones in the northern as well as in the southern extra-tropical regions. 
Further, it is well known that these facts may be accounted for by the 
similar climates in similar latitudes, by the changing of area of hekisto- 
thermic or mesothermic plants during the glacial period or after it, by the 
wholesale extinction of species during that period owing to lack of resistance 
or their inability to adapt themselves to the new conditions of life. 
Still, there remains a large number of cases of species or nearly allied 
ones which are disjointedly distributed in meridional direction across the 
equator. Sir Joseph Hooker, in his memorable Introductory Essay to the 
Flora of Tasmania, was the first to call attention to the species occurring 
at the south corner of America which are identical with those of the arctic 
or northern temperate zone. The same author was the first to give a list of 
the so-called European types on Cameroon Peak. 
Later on, species of the same character were found on the Kilimanjaro 
and other high mountains of tropical East Africa. 
As a result of the botanical investigation of Africa, a considerable 
number of highland forms have been recorded whose nearest relatives are 
to be looked for partly in the boreal region, partly in other widely separated 
countries. Also at lower altitudes several species are to be found which 
appear in regions far distant from Africa. 
In regarding those plants, the following questions must always be borne 
in mind : 
i. Are they identical with the forms living in other latitudes, or do 
they show any small variation from them ? 
[Annals of Botany, Vol. XVIII. No. LXXII. October, 1904.] 
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