The Extra-floral Nectaries of the Genus Polygonum. 
BY 
E. J. SALISBURY, B.Sc., 
Qiiain Student in Biology {Botany), University of London, University College. 
With Plate XVI, and six Figures in the Text. 
T HE present research was undertaken with a view to ascertaining the 
function of the glands which occur on the underside of the leaf- 
cushion in various species of Polygonum. The following species have been 
under observation, viz. : — 
Polygonum baldschuanicum , P. cilinodum , P. compactum , P. Convolvulus , 
P. cuspidatum , P. multiflorum , P. sachalinense , and P. scandens. 
All the above agree in possessing leaves which are variations upon the 
cordate-saggitate type and are either herbaceous or annual. 
The only woody species is P. baldschuanicum , which produces climbing 
shoots that die back in the winter. Polygonum cilinodum , P. Convolvulus , 
and P. scandens are also of climbing habit. 
The extra-floral nectaries of P. cuspidatum have been described by 
Delpino (5) ; those of P. baldschuanicum, P. Convolvulus , and P. multi- 
Jlorum by Schwendt (15), and those of P. sachalinetise by Ono (12). The 
two latter papers were published during the course of the present research. 
Detailed descriptions of the above species need not therefore be included. 
For convenience, the paper is divided into the following sections, 
viz. I, General; II, Special; III, Microchemical; IV, Physiological; 
V, Summary and General Conclusions. 
I. General. 
The extra-floral nectaries are oval, triangular, or circular depressions. 
In all except the circular nectary of P. cilinodum the depressions are boat- 
shaped. The nectaries lie in the plane of symmetry of the leaf and are 
situated upon the underside of the base of the petiole just below the 
abscission layer which is differentiated at an early stage (PL XVI, Fig. 4 ). 
Polygonum cilinodum is, however, an exception to this rule, for in this 
species where, though the glands were fully developed, no abscission layer 
could be recognized. Like most nectaries these stand in close relation 
[Annals of Botany, Vol. XXIII. No. XC. April, 1909.] 
