328 ZONES AND REGIONS [Pt. Ill, Sect. I 



These orchids, owing to the mode of spreading their organs, are principally 

 adapted to light from above. The same holds good for manj' epiphytic ferns. 

 The widespread and very common Asplenium Nidus occurs under very various 

 degrees of illumination. Wiesner observed for it; L = 1/4 up to 1/3S (I maxi- 

 mum = 0-4-0-042). 



Epiphytes whose vegetative organs lie flat against the bark are adapted to light 

 from the front. Hence in the Buitenzorg garden, the otherwise common Taenio- 

 phyllum ZoUingeri, Reichb. f., a small leafless orchid with assimilating roots pressed 

 close to the bark, does not grow in the orchid quarter, because the light from the front 

 is too weak. Wiesner has communicated the following, as a result of numerous ob- 

 servations made by himself, regarding the degree of light demanded by this plant :— 



LIGHT-REQUIREMENTS OF T.AENIOPHYLLUM ZOLLINGER!, 

 REICHB. F. (after Wiesner). 



L. J nHi.viiintiii. I mean. 



Limits of development \l1~\ly2. o-533-o-o5o o-i66-o-oi5 [ 



Most vigorous development \It-\I<^ 0'228-o-i77 0-07 1-0-055 j 



Arrest resulting from insufficient intensity of light . 1/32 0-050 0-015 



Arrest resulting from too intense light . . . 1/2-1/3 o-8ii-o-533 c-25i-o-i66| 



Flowers were observed with 1/5-1/S 0-320-0-205 0-101-0-063 



Besides the epiphytes belonging to the Phaneroganiae and the Pterido- 

 phyta which alone have been dealt with so far, the tropical virgin forest 

 also possesses others among Algae, Fungi, Lichenes. and Br}-oph}'ta, anc 

 many of these plants, in particular some Hepaticae, also show a high degree 

 of adaptation to the substratum. Whilst the occurrence of such lowei 

 cryptogams on the bark of trees is also exhibited in temperate forests, anc 

 actually to a far greater extent than in tropical forests, their appearance a; 

 epipJiylloiis forms, that is epiphytic on leaves (Fig. 170), is apparentl) 

 confined to the tropics. Epiphyllous forms are quite common features 

 particularly on ageing leaves, in very humid rain-forests. 



The epiphytic plants on a tree in a virgin forest are not the same fron 

 its base to its topmost branches, but exhibit a well-marked differentiation 

 Low down on the trunk are many plants that are also terrestrial, such a| 

 species of Hymenophyllaceae, Carludovica, climbing Araceae ; ascendin;! 

 higher, these indifferent forms disappear, and the xcrophilous characteii 

 otherwise foreign to the rain-forest, increases with the increasing adaptatioi 

 to an epiphytic habit (Fig. 171), so that the epiphytic species met witH 

 which occasionally also occur on the ground, appear to be plants of verj 

 dry stations, and, to some extent, of stations with strong illumination. Th! 

 epiphytes on the highest branches and consequently those that are mo& 

 insolated are identical with those that form the aerial flora of well-lighte 

 woodland and of the savannah of dr)' open districts. Hence after the partij 

 clearance of the forest, the epiphytes on the lower portions of the trees tha 

 are left standing die, whilst those on the crowns gradually spread dowrl 





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