2'rati8action». 145 



all over the world ferns (cryptogams, (fee, 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 efiect 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 clijaber, 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 its extension. 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 cliuibing 

 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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