The Leaf Glands of Dioscorea macroura, Harms. 
BY 
MATTHEW YOUNG ORR. 
With Plates CXCVII-CXCVIII and Three Figures in the Text. 
Dioscorea macroura, the peculiar leaf glands of which have been 
made the subject of an extended research by the writer, is a 
West African species, and a native of the tropical rain-forests 
in the region bordering on the Gulf of Guinea, 
First collected by Zenker in the Cameroons in 1891, it was 
described as a new species by Harms in 1897. In his diagnosis, 
which appeared in the Notizblatt* at Berlin, Harms lays par- 
ticular emphasis upon the extraordinary development of the 
acuminate leaf-apices, which he refers to in the following 
terms :—‘‘tiberall tritt an den Blattern eine auffallig lange, 
schmale, mehr oder minder scharf abgesetzte, verdickte, 
schwanzartige Spitze hervor.’’ ‘This highly developed acumen 
presents its most interesting aspect, however, as a study in 
physiological plant-anatomy, for in its internal construction 
there appear features that are perhaps unique within the genus. 
Its chief point of interest lies in the complex glandular system, 
which traverses its length from base to apex, and which differs 
markedly from the ‘‘sunken glands”’ of other species, so fully 
described by Correns + in his work on the extra-nuptial nectaries 
of Dioscorea. Moreover, the mucilaginous secretion which fills 
the lumen of these glands harbours a species of bacterium, which 
is always present in great numbers, even in the living leaf. 
This constant association of a bacterium with the secretory 
organs of Dioscorea macroura is not without a certain physio- 
logical import, and may prove to have a direct bearing on the 
economy of the plant. In this, and in certain other features, 
the glands of this species certainly show a striking resemblance 
to the ‘‘bakterienknoten’’ found in the leaves of other tropical 
plants, the essence of which, according to continental investi- 
gators, is a symbiotic union between the plant and a ah 
micro-organism. Among the recorded oe of ‘*bakteri 
* See Notizbl. k. bot. Gartens u. Mus. zu Berlin, i. (1897), p. 2 
+ C. E. Correns in Sitz. Ber. Math. Nat. Cl. Akad. Wien. Lege Sk: 1 (1889), p. 651. 
(Notes, R.B,G., Edin., No. LXVIII, November 1923.] 
