258 Journal of the Asiatic Society of Bengal. [N.S., XIII, 



well above the uppermost leaves ; the other, which is found on 

 the banks of streams and in the moist ground that borders a 

 wood, has the inflorescence condensed into a rounded mass close 

 down on the top pair of leaves. 



Coming now to shade-loving plants a definite difference in 

 . the position of the leaves when compared with those of the 

 open downs has already been noticed. They are also in general, 

 as would be expected, much larger than in the open, though not 

 always so. The flowers are either small and inconspicuous or 

 large and white. This is well illustrated in the small epiphytic 

 orchid Eria braccata, Lindl. which from a flat tuber not half an 

 inch across bears solitary white flowers over an inch hi diameter : 

 and also in two epiphytic species of Coelogyne. C. nervosa, A. 

 Rich, and C. odoratissima, Lindl. when compared with C. glandu- 

 losa, Lindl. which grows on open rocky slopes. 



These epiphytic orchids have, as often happens, tubers in 

 which water is stored, and in Eria braccata, Lindl. (E. reticosa, 

 Wight) the tubers which are quite small, less than half an inch 

 across, are covered with a raised network of v. icular bundles from 

 between which the parenchymatous tissue has decayed away. 

 This fine network would hold water that ran down the branch 

 of the tree on to the tubers. Two orchids which grow on ex- 

 posed and rocky slopes are sharply contrasted in regard to 

 their water-storing adaptations. Coelogyne glauclulosa, Lindl. 

 has large banana -shaped tubers which swell during the rains 

 and slowly shrink in the dry weather. Aerides crispum. Lindl, 

 which grows in much the same sort of locality, has no tubers, 

 but the long thick roots run laterally along the natural ledges 

 of rock and form a collecting ground for soil and debris washed 

 down from above. In the earth so collected various small 

 herbs and grasses take root and form a compact sod. two to six 

 mches deep, in which water is most effectively retained and 

 easily available for the orchid. The root of this plant have a 

 velamen exactly similar to that of epiphytic Bpecies, in which 

 alone the velamen is usually the subject of notice. It ems 

 probable that the usually accepted explanation of the value 

 and function of the velamen should be modified and that it 

 should be regarded not merelv as a modification for the special 

 purpose of absorbing intermittent rainwater, but also as being 

 an absorptive tissue of use to roots in soil ; and of special value 



as being much less easily damaged bv dessication than are the 

 root-hairs. 



These orchids seem also to illustrate the direct effect of illu- 

 mination on distribution. The two species of Coelogyne men- 

 tioned as shade plant occur, as far as I know, onlv as epiphytes 

 in the shade of trees ; one, that just mentioned, onlv on absolute- 

 ly open rocky slopes. Of Aerides also one species, A. radicosum, 

 a mch., is only an epiphyte, the othe A. crispum Lindl. grows 

 only on sunny rocks. The leaves, stem tubers and other 



