756 RELATION OF STRUCTURE TO FUNCTION IN ROOTS. 



buttresses, with regular radiating arrangement around the trunk, inclosing small 

 niches, much sought after as hiding-places by various animals, and offering very 

 acceptable holes to foxes, for instance. In point of fact, these roots are often called 

 " buttress-roots ". Tabular roots are a peculiarity of tropical trees with huge, heavy 

 crowns. A particularly well-defined form is exhibited by the West Indian Cotton 

 Tree (Eriodendron caribceum) and by the India-rubber Fig (Ficus elastica) belong- 

 ing to tropical Asia, and yielding caoutchouc. The picture of this tree, drawn from 

 nature by Ransonnet, fig. 185), gives us a very clear idea of these tabular or buttress- 

 roots; the same figure, in the background to the right, also shows another species- 

 of Ficus, viz. the celebrated Banyan-tree (Ficus Indica), which will be described 

 presently. 



Stilt-like roots (radices fulcrantes) also arise in the same way from the erect or 

 oblique main trunk, but they are cylindrical, and have the form of oblique props. 

 Sometimes the oldest, lowest portion of the erect trunk thus supported dies away, 

 or the disintegration may be continued some little distance up, so that only the 

 upper part of the stem remains fresh and living. The first roots of mangrove 

 seedlings (illustrated on p. 605), which penetrate the mud, have also the power of 

 raising the trunk to which they belong up above the mire by their growth in length. 

 These trunks then look as if they were on stilts, and are only connected with the 

 ground by means of the roots. On page 758 we have a figure of the Screw 

 Pine (Pandanus), and in fig. 187, of a species of mangrove, in both of which these 

 odd root-structures are seen. They are also to be found in many other plants of 

 the tropics, viz. in palms, Clusiacese, and fig-trees. In some clusias the stilt-roots- 

 are thicker than the stem they support, and in the mangroves, growing in crowded 

 forests on the sea-shore, where they are exposed to the ebb and flow of the tide, 

 they branch and fork continually, forming a tangled confusion, the strange appear- 

 ance being heightened by the fact that all the root-branches and stems, up to the 

 level of the water at high tide, are covered with an armoured coat of various 

 molluscs and crustaceans. 



Columnar roots (radices columnares) originate from horizontal or obliquely 

 ascending branches of trees, and grow vertically down until they reach the ground. 

 They then penetrate into it, unite with the soil, and thus form pillars on which the 

 widely projecting boughs of the tree are supported. Trees whose erect trunks are 

 supported by tabular roots and those which are provided with stilt-roots may at 

 the same time develop columnar roots from their branches. One of the oblique 

 branches of the India-rubber Fig, illustrated in the foreground of fig. 185, is- 

 seen to be supported by a huge pillar, which gets thicker towards the base, whilst 

 the mangroves figured on pp. 605 and 759 also exhibit long, supporting roots passing 

 down from the lower horizontal branches of the crown, which push in between the 

 stilt-roots, and grow down into the mud. Not long ago these mangrove roots were 

 thought to grow out of the fruits while these were yet hanging on the trees, and 

 to grow lower and lower until finally they reached the swampy ground. It is, 

 of course, true that the embryo grows out from the fruits while they are hanging 



