6 BOTANICAL GAZETTE [JANUARY 
vegetation. Geologically speaking, only a short time ago the 
glacial period made a clean sweep over wide areas, and deci- 
mated the vegetation of neighboring regions, so that when it was at 
an end nature had to begin planting the ground anew. This surely 
is one of the causes of the poverty of species here in the north. 
Most likely other causes of a physical nature also exist. So far 
as I can see, the vegetation here in Scandinavia and even in the: 
higher north might really have been much more rich in species 
than now is the fact; only it has had no time for that, but for 
every century or, better, millenium that passes, other species, 
even without the help of man, will immigrate and mix them- 
selves with the old ones, and new species will arise. 
Of course this variety, which is one of the characteristics of 
tropical nature, also shows itself through “rat immense mass of 
curious ecological adaptations which we know or eagerly try to dis- 
cover. There is a great difference between the objects of 
botanical exploration during the first five or six decades of this 
century, and those of the later decades. It was Darwin’s monu- 
mental work that led science into new ways. Formerly the 
botanists especially wished to discover the many unknown 
genera and species. Now it is Xf itself they wish to study, 
those wonderful relations of the varied and often very compli- 
cated reciprocity of action between living beings, of which a 
great deal is already known, such as mimicry, the fecundation 
of plants by insects, the adaptation of epiphytes and other 
plants to surrounding nature, ant-loving plants, insectivorous 
plants, parasitism, and other ecological facts. These are mostly 
to be looked upon as directly and entirely independent of climate 
and other physical conditions, while the number of them will 
hardly be understood, unless, as Wallace has done, we take into 
consideration the probably uninterrupted process of develop- 
_ ment of tropical nature through geological periods. 
Now we must acknowledge that within the tropics the rich- 
ness of forms is different in different situations. Even the small 
Lagoa Santa shows a striking example of this, for the forest is 
twice as rich in species as are the campos, although the area of 
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