r 47 ] 



V. 



NOTES ON THE POLLINATION OF CERTAIN SPECIES OF 

 DENDROBIUM. 



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



[communicated by professor H. H. DEXON, SC.D., F.R.S.] 



Read December 22, 1908. Ordered for Publication January 12. Published Apkil 3,1909. 



Plates V. and VI. 



The following notes were made in northern Siam, either on orchids growing 

 naturally, or on specimens removed from the neighbouring jungles to my 

 garden for convenience in observation. 



As I was able to work out most fully the mechanism of pollination in 

 Bendrohium Dalhousieanum Paxt., and as its mechanism is typical of that of 

 many other species of Dendrobium, I will give my observations on that 

 species first. 



Dendrobium Dalhuusieanum has large flowers with a spreading perianth. 

 The lip is large and concave, with a patch of fimbria on its tip ; posteriorly 

 it is produced into a short spur, which contains the nectary. A passage, the 

 roof of which is formed by the column, the sides by the sides of the lip, and 

 the floor by the disc of the lip, leads to the nectary. Hereafter I shall 

 refer to this portion of the flower simply as the passage. The direction of 

 the passage is upwards and backwards. Owing to a thickening of the disc, 

 the floor of the passage rises posteriorly till it meets the roof, thus blocking 

 the entrance to the nectary. There are three longitudinal ridges on the 

 disc, which end abruptly before the column is reached. A slight weight on 

 the lip depresses it sufficiently to allow of the entrance of a proboscis into 

 the nectary. A reference to Plate VI., fig. 1, which represents a longitudinal 

 section, slightly to one side of the median line, through the column and base 

 of the lip, will explain the structure of the flower more clearly. The anther 

 has a thin free edge pointing backwards and slightly overlapping the 



SOIENT. PBOO. E.D.S. , VOL. XII., NO. V. K 



