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XXIV. 



NOTES ON DISCRIDIA RAFFLE8IANA, Wall., and 

 DISCHIDIA NUMMULABIA, Br. 



By a. F. G. KEER, M.D. 



[oommunicatkd by professor h. h. dixon, sc.d., f.r.s,] 

 [Eeatl March 2C. Published Septemper 30, 1912,] 



(Pr.AiRs XXV.-XXXI.) 



Habit and General Morpholoyy. 



Bischidia raffiesiana, Wall., and Bischidia nummular ia, Br., are common 

 epiphytes in the dry, deciduous jungles of Northern Siam, particularly in 

 " Eng " jungle. Bischidia raffiesiana is most commonly found on Bipterocarpus 

 tuherculatus, Roxb., the predominant tree of this jungle, but by no means 

 exclusively so ; S/iorea ohtusa. Wall., Pentacme siamensis, Kurz, Melanorrlma 

 usitata, Wall., Eugenia friiticosa, Roxb., Bridelia refusa, Spreng., and other 

 deciduous trees also act as hosts. Bischidia nummularia is found on nearly all 

 the trees of this jungle ; it also extends into jungles containing both 

 deciduous and evergreen trees. 



In accordance with their mode of life, both these epiphytes show decided 

 xerophilous characters. 



B. nummularia has fleshy, orbiculai", yellowisli-green leaves, 1 to r4 cm, 

 in diameter ; they are biconvex, though, as a rule, somewhat flatter on the 

 lower surface, which lies on the bark of the host. The epidermis has a 

 thick, waxy cuticule. The plant is attached to the host by adventitious 

 roots arising from the ventral surface of the stem, a pair springiug from eacli 

 node close to the insertions of the petioles. Once I observed an additional 

 root from the dorsal surface of a node, comparable to the pitcher roots of 

 B. raffiesiana, to be described later. The roots serve as organs both of 

 attachment and absorption. Adventitious roots appear at a very early stage 

 in the life-liistory of the plant; with the expansion of the cotyledons 

 the primary root ceases to develop and begins to wither, while adventitious 

 roots are developed from the swollen lower portion of the hypocotyl. 



When a plant grows in a shady situation, the leaves are thin, flat, more 

 elliptical in shape, less thickly coated with wax, and of a more decidedly 



SCIENT. PEOO. R.D.S., VOL. XIII., NO. XXIV. 2 Z 



