Sunshine, Rain, and Wind 
On Cologne Cathedral one can see rosebushes and 
privets which have been there established by birds.! 
On many stone bridges one may find tiny plants of the 
black maidenhair, which are not to be discovered any- 
where else within several miles. Other cases are the 
well-known alga of the snow, and the curious gossamer- 
like snow-mould, which seems to be only found on 
decaying vegetable matter in the hollow formed by a 
thaw between the snow and the earth5 
There are certain plants in the Amazons which only 
occur in the “ gardens” formed by intelligent ants and 
soon. Such examples show how ingenious plants may 
be in adapting themselves to the strangest existences, 
In order to live under such special and peculiar 
conditions, great changes are required not only in 
the outward form of leaves, stems, and roots, but also 
in microscopic structure. The peculiarities of desert 
plants and water plants belong rather to the botany of 
ten years ago, and have been thoroughly studied by 
Henslow and many others,® 
There are two different methods which have been 
used by various botanists of late years in the study of 
environment. One may take one particular genus, say 
the oak tree, and study the leaves of every species of 
Quercus in the world in connection with the various 
climates in which those species are found.” Or one 
may take some particular kind of habitat or climate and 
distinguish the type or types of leaf that seems to pre- 
dominate under those special conditions. 
The great work of Dr. Hansgirg on the shapes of 
leaves is an instance of this last method. As no one 
has ever studied leaves with the same thoroughness and 
wide experience, he has certainly earned the right to 
generalise, and his conclusions are therefore of great 
importance. According to him, the object of every 
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