IN BORNEAN FORESTS [chap, hi 



as an arrow, is generally of a grey colour, caused by the lichens 

 which grow on it. 1 



Most of the plants and fruit-trees I have mentioned do not 

 grow in and about Kuching with that vigour which the luxuri- 

 ance of the neighbouring forest would lead one to expect. The soil 

 of the low hills on which Kuching is built, and also that of the adjoin- 

 ing land, is formed of white or yellowish clays, and is far from fertile 

 — which one would hardly suspect, or, indeed, think possible, con- 

 sidering the giant proportions attained by trees on the same area 

 before the forest was cleared. The explanation probably lies in 

 the fact that the forest trees depend mostly for their growth not on 

 the soil formed by the decomposition of rocks, but on the vegetable 

 humus, the result of centuries of accumulation. 



The first months of our stay in Sarawak passed rapidly ; many 

 and varied occupations made the time seem short. It was with 

 difficulty that I found time to prepare and dry the numerous plants 

 which I collected daily in the adjacent forest. The number of species 



1 In Borneo I found foliaceous lichens excessively rare ; most of those 

 which I collected there, about 140 in number, were encrusting species, which 

 blend with the bark on which they grow. They were principally Graphidece, 

 Thelotrema, Ascidinece and Verrucaria. (Cf. Krempelhuber. Lichenes quos 

 legit O. Beccari in Insulis Borneo, etc., in Nuovo Giornale Bot. Ital., 1875, p. 6.) 

 A large portion of these lichens were found by me in the grounds of Govern- 

 ment House on the trunks of arecas, coconut palms, orange, and shaddock 

 trees. It appears, therefore, that, in Sarawak, trees with a smooth bark, in 

 open localities with plenty of light, are best adapted to support lichens ; for 

 in the shady forest they are much less frequent on tree trunks, but abound, 

 together with various Fungi and Jungermannias, on the leaves of low-growing 

 species. The reason of this predilection shown by hchens for the smooth 

 bark of trees growing in the more open spaces is, I suspect, to be sought in 

 the greater facility of the condensation of aqueous vapour on certain surfaces 

 in preference to others. The non-porous, smooth, and compact surface of the 

 bark on the trunks of coconuts, arecas, and orange trees growing in the open, 

 which becomes much heated during the day, radiates greatlv at night, and, 

 in cooling, causes the aqueous vapour with which the atmosphere is laden to 

 condense in abundance. This moisture remains, moreover, better on these 

 smooth barks than on those of a cork-like or porous nature, far less good 

 conductors of heat, and more easily absorbing the aqueous vapour. A smooth 

 and non-porous bark may be compared with a rock, on which encrusting 

 lichens nourish well ; for these organisms require periods of moisture, alter- 

 nating with seasons of drought, in well-lighted localities, rather than an excess 

 of moisture of a continuous nature in shady places. I imagine that such is the 

 reason why many epiphytes, and amongst them orchids, prefer to take root 

 on naked smooth-barked trees, often in the highest and most exposed parts, 

 where at first sight one would think that their seeds must find great difficulty 

 in germinating. Smooth and coriaceous leaves must likewise condense the 

 aqueous vapour of the air much more easily than leaves which are hairy and 

 soft in texture ; and it is for these reasons, perhaps, that a large number of 

 Hepaticae, and both encrusting and foliaceous lichens, are often found on the 

 upper surface of such leaves in the low-lying parts of the Malavan forests. 



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