Transactions. 145 
all over the world ferns (cryptogams, &c., lower in the scale 
than flowering plants) are chiefly found in it. The English 
character is very interesting. To find a thalictrum under 
the line means that at some time a chain of European 
climates, perhaps as mountain tops, extended from Europe to 
Central Africa, or that by some extraordinary shifting of seas, 
or of the earth’s axis, a temperate climate extended all over 
Africa north of the Equator. Of course one may say that a bird 
in its migration brought these seeds, and that, the climate being 
favourable, they grew and flourished. The other characteristics 
are more interesting to explain. If one grows a plant in the 
shade the effect of moisture and the absence of light is to produce 
a long drawn out stem and distant leaves ; thus a daisy grown in 
wet shade will produce a long stem with leaves scattered along 
it instead of a tuft of leaves. Now, such a long drawn out stem, 
the top of which will (in accordance with known laws of growth) 
rotate, is simply nothing but an embryo climber, and hence we 
can understand how so many plants have taken in the climbing 
habit, and many others by growing long branches are caught and 
upheld by other plants, are, of course, directly induced to do this 
by the same reason. This climbing habit is one eminently 
suitable to a forest, and thus Nature has directly produced the 
most favourable form. The cordate form of leaves is one most 
often associated with climbing plants, and seems to depend on 
the length of the petiole and the hang of the leaf, but the 
explanation of this form has not been given as yet. The large, 
thin, membraneous character is, however, directly produced by the 
absence of strong sunlight, which, by forming a strong cuticle 
outside the leaves, prevents itsextension. This thin, membraneous 
character and large size, as well as the length of the internodes, 
are again all directly favourable to the conditions, for the light 
is very diffused, and the larger the leaf the more it will catch, 
The object of the leaf is not to avoid being scorched, as in a 
sunny climate, moreover, the more spaced the leaves the less they 
will interfere with one another. The trees senecios and veronias 
have simply taken to forming tree stems instead of climbing 
stems like their relations (millanias, &c.). There are few thorns, 
probably because a cold, wet climate is unfavourable to their 
production, just as a hot, dry climate tends to produce them in 
the most unusual orders of plants. There are also very few 
antelopes or leaf-feeding beasts of any kind, so far as I know. 
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