342 MESOPHYTES SECT, xvi 



ADAPTATIONS 



Tree-form. The majority of trees show nothing remarkable in their 

 shape, but some forms encountered are worthy of note. Haberlandt l 

 has mentioned and figured some of these, including the umbrella-form, 

 the candelabra-form, the tiered-form ; but several others might be men- 

 tioned, including the palm-form. The mode of branching is far more 

 diversified, and apparently more irregular than in the trees of northern 

 Europe ; very commonly the twigs bear clusters of leaves only near their 

 ends, and each stem emits only few branches. 2 



Roots. Plank-buttresses are formed by the roots of many species. 

 These buttresses are much taller than they are thick, and are continued 

 up from the base of the trunk, sometimes to a height of two or three metres, 

 as large, often bent, plank-like growths. The cross-section of the trunk 

 immediately above the soil thus acquires a stellate shape, and the space 

 round the base of the trunk is divided into stalls. These roots provide 

 firm and broad foundation for trees that possess huge trunks and large 

 crowns. Such plank-buttresses occur in certain species of Bombaceae, 

 in Ficus, Myristica, Carallia, Sterculia, Canarium, and others. According 

 to Schimper they are particularly characteristic of humid forest, and are 

 wanting where the rainfall is small. 3 



Prop-roots similar in design to those of Rhizophora 4 are possessed 

 by Iriartea and some other palms, and by Pandanus. They are terete 

 flying buttresses springing from a certain height up the trunk, descending 

 at acute angles to the ground, and showing a radiating arrangement 

 similar to that in Rhizophora. The number of such props possessed by 

 a tree is sometimes considerable, for example, more than twenty. In 

 another guise prop-roots occur on Ficus religiosa and other trees, as they 

 spring from the boughs and enable a single tree to spread over a vast area, 

 and produce a forest which has an extremely thick canopy of leaves and 

 casts deep shade. It is this shade that may possibly be the cause of the 

 luxuriant growth of the roots in question. 



Bark. The cortex is thin, but otherwise varies greatly. In this respect 

 a sharp contrast is provided by trees growing on the Brazilian campos, 

 for these have very thick coats of cork and cortex, though they may be 

 growing only a few metres away from the forest-trees. 5 



Thorny stems. Thorny stems are not uncommon, and occur in Hura, 

 Erythrina, and others, but are commonest in palms. In addition one 

 encounters trees, such as Xanthoxylum, with peculiar laminated cones 

 of cork occurring on their stems. 



Buds. The, buds do not possess dry bud-scales such as occur in the 

 trees of northern Europe, or, at most, bud-scales are infrequent and 

 mainly encountered in drier forests. 6 The buds are protected by stipules, 

 leaf-sheaths, and outgrowths of the petiole ; in addition water, resin, or 

 mucilage is often excreted between the bud and its envelope. 7 



Flowers. Remarkably few flowers are to be seen, although tropical 

 forest always abounds in flowers, which are as a rule high overhead in the 



1 Haberlandt, 1893. 2 See the figures of J. Schmidt, 1903. 



3 See also Whitford, 1906. * See p. 236. 6 Warming, 1892. 



* Warming, loc. cit., figs, on pp. 409-11. 

 ' Percy Groom, 1892; Schimper, 1898; Raunkiar, 1905, 1907. 



