OrR—LEAF GLANDS oF DIOSCOREA MACROURA. 71 
On the other hand, this association of a bacterium with 
Dioscorea macroura has every appearance of being of the nature 
of a more permanent alliance, for, as it has been pointed out 
already, the organism is present in the secretion enveloping the 
bud which originates from the tuber, by which avenue it 1s 
apparently able to reach the developing glands of the new plant. 
All attempts to grow the plant from a sterilised tuber, under 
perfectly sterile conditions, have so far proved abortive, and it 
is therefore impossible to say what effect the disassociation of 
bacterium and plant would have upon the growth of the latter. 
Although dissimiiar in structure and mode of origin to those 
of Ardisia, Pavetta and Psychotria, the leaf-glands of Dioscorea 
macroura undoubtedly possess some of their peculiar physio- 
logical properties. They have been shown to differ in many 
ways from the extra-nuptial nectaries of other species of 
Dioscorea, and in one particular—their bacterial nature—they 
are possibly unique within the genus. 
In conclusion, the writer desires to record his indebtedness to 
Dr J. M. Dalziel, for much helpful information regarding the 
plant in its native habitat, and to Mr I. H. Burkill, Director 
of the Botanic Gardens, Singapore, for his invaluable assistance 
in the matter of identification. An expression of thanks is also 
due to Mr R. M. Adam, for the photograph of the culture, 
reproduced on Plate CXCVIII., and to Mr J. J. Campbell, for 
the care expended on the cultivatién of the plants, which 
furnished the material for this investigation. 
SUMMARY. 
1. The leaf-glands of Dioscorea macroura form a series of 
elongated “ pockets”’ in the mesophyll of the prominent acumen. 
2. The ‘‘pockets’’ are formed by a process of invagination 
followed by subdivision, and when mature communicate with 
the upper epidermis by way of narrow slits or ducts. 
3. Each glandular ‘‘pocket’’ is lined, in part, with a secre- 
tory tissue composed of vermiform, multicellular trichomes, and 
is filled with a mucilaginous fluid which gives a strong proteid 
reaction. 
4. The fluid content of the gland cavity is the home of a 
bacterium which is always present in great numbers in the 
glands of the living leaf. ; 
5. The bacterium, when isolated in pure cultures on artificial 
media, is found to possess the power of nitrogen-fixation to an 
appreciable degree. 
. The nitrogen-content of the glandular acumen 1s greatly 
in excess of that of the leaf-lamina, postulating a similar process 
of nitrogen-fixation taking place within the glands 
