General 
If, then, one were prepared to speculate on the original 
settlement of the earth by the plant world, one would 
expect the dry land to have been occupied by, jirst, 
Alge, Fungi, and Lichens; 2. Mosses; 3. Ferns; 4. 
Flowering plants in an open flora such as one sees in 
a desert, in Tibet or in the Arctic Regions; 5. A close 
flora of small shrubs; and 6. Trees or a wood asso- 
ciation. 
At present the development of flowering plants has 
reached such a stage that they grow almost every- 
where, and are adapted to all sorts of climates and 
conditions; and yet we find in the colonisation of 
these lavas, hints which seem to explain the old original 
process.* 
Something of the same succession can be traced even 
now on mountain sides and in the Arctic Regions. 
For, as we shall see in another place, lichens occur on 
boulders or bare rockin far Northern latitudes, also on 
mountain ridges where not even mosses can manage to 
exist. An open or scattered flora of small half shrubby 
plants characterises both the highest Alpine and most 
arctic conditions. Heather moors extend farther up 
the mountain side and more to the north than trees; 
and even amongst trees, coniferze, which are relatively 
older and less complex in structure than the deciduous 
trees, are often found as mountain and northern woods, 
when the lowlands are occupied by oak forest or other 
deciduous woods, 
So that if one assumes that the plant world even 
to-day is proceeding with, but has not finished its task of 
occupying the far north and mountain summits, then we 
see in every case a higher and more advanced kind 
* Tropical lavas show blue-green Algze, Ferns, Rock plants, Shrubs, Jungle. 
Temperate lavas show Lichens, Mosses, Open Flora, Shrubs, Trees, Old 
walls show Lichens, Mosses, scattered Herbaceous plants. 
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