ROOTS OF EPIPHYTES 129 



the bark, absorb some of the water that runs down 

 the branches and trunk of the tree after every 

 shower, and also any mineral matter that may be 

 blown up from the ground as dust, and be dissolved 

 in it. But being entirely unconnected with the ground, 

 this, and the little rain that actually falls on them is 

 all these plants get, and therefore as one might ex- 

 pect, they grow only where the air is moist and rain 

 falls frequently. On the roads of Singapore which 

 has a very damp climate, almost every tree has on it 

 some often very many epiphytic ferns. In addition 

 to these clinging roots, some epiphytes (not ferns) have 

 others which are about the thickness of an ordinary 

 lead pencil, and hang down freely, being apparently 

 quite insensitive to light, or if any thing, attracted 

 not repelled by it. The orchid, VANDA ROXBURGHII, 

 is a fairly common Indian epiphyte which has these 

 roots well developed. When dry, the root looks quite 

 white, but if moistened, greenish. Breaking it with 

 the fingers, one can easily separate the soft outer white 

 part from a firmer central part. This soft outer 

 portion, is composed of very loose spongy tissue, with 

 lots of little spaces empty of everything except air, 

 and looks white for the same reason as the foam of 

 the sea, or the froth on fermenting toddy, looks white, 

 that is, because the light is reflected in all directions 

 from numbers of tiny bubbles of air. When this 

 tissue is wetted, the air is replaced by water, and it 

 becomes more or less transparent so that the green 

 colour of the central part shows through. 



This aerial root then differs from all ordinary roots, 

 in having a green layer overlaid by a spongy one. 

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