APPENDIX 



mostly entire, coriaceous, and shining on the upper surface. Big leaves, 

 however, are to be seen in certain Sterculiacece, Bombacece, and Diptero- 

 carpece, etc. On the summits of mountains in Borneo most of the shrubs 

 have small leaves. Acicular, narrow, long, rigid or phyllodiform leaves, 

 so frequent in plants of Australasia, are very rare. 



The surfaces of the leaves of the plants of the primeval forest vary 

 greatly. Often they appear as if coated with varnish above and covered 

 with small scales or dense wool beneath. It does not appear to me 

 impossible that similar structures, besides having a moderating action 

 in regard to evaporation, are useful as a defence against parasitical 

 fungilli, preventing the penetration of spores into the tissues. If the 

 plants of our climes had to pass a summer in an atmosphere like that of 

 Borneo, they would at once be invaded by cryptogamic vegetation, 

 as indeed happens in our own country when we have a warm, damp 

 summer. Within the tropics fungilli affecting the inner tissue of growing 

 leaves are rare. At every step in the forest, however, minute forms of 

 inferior plants are to be seen, such as lichens, mosses, HepaliccB, or Algce, 

 which vegetate on the surface of living leaves, without damaging the tissue 

 on which they grow. 



Plants with Variegated, Metallic, or Brightly Coloured Leaves. — The 

 plants which are most beautiful on account of their variegated leaves, 

 and bright, metallic, or intense green coloration, live in the humus 

 where the forest shade is dense. To their number belong various 

 species of Aracece, Melastomacece, Cyrtandracece, Rubiacecs, Orchidece, 

 etc., which show a leaf-coloration far more brilliant than congeneric 

 species which grow in the sunshine, a fact which appears to be in direct 

 contradiction with another, for it is well known how plants kept in the 

 dark fade and lose their colour. Yet whilst plants generally fade and 

 become etiolated when kept from light, those with leaves of a deeper 

 green and more bright coloration prefer shady spots. 



It is well known that the green coloration in plants is caused by an 

 immense number of minute granular corpuscules enclosed in the tissue 

 cells, which owe their colour to a pigment known as chlorophyll. These 

 corpuscles are a product of the protoplasm, viz. of the essential living 

 and sensitive portion of the vegetable cells, and have the faculty of 

 moving about within the walls of the cell which includes them, and of 

 modifying their shape, by reason of the vitality and sensitiveness of the 

 protoplasm in which they are embedded. A very strong light causes 

 the chlorophyll granules to hide away, crowding together in the deeper 

 portion of the tissues, whilst diffused light is favourable to a uniform 

 distribution of the granules. It is well to bear in mind these details 

 of the minute and microscopic structure of plants, because it seems likely 

 that leaves naturally silver- spotted, marbled, or variegated owe their 

 peculiar coloration to the faculty possessed by chlorophyll granules of 

 grouping themselves together in various ways according to the manner 

 in which light influenced the leaves during the most remote plasmative 

 epoch. According to this hypothesis, marbled and variegated leaves 

 would be merely the hereditary reproduction of the above-mentioned 

 phenomenon, which must have occurred when (in the period when the 

 stimuli could produce permanent effects on organisms) the thin solar 



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