230 Salisbury .— The Extra-floral Nectaries of the 
to the vascular system. The vascular supply of the petiole is therefore of 
some interest and attains greater significance when viewed in the light 
of the physiological experiments to be described later on. In general, the 
petiole of the Polygonums is convex or angled upon its lower surface 
and concave or grooved upon its upper. 
The bundles form a dorsal arc which is closed by a bundle or bundles 
placed ventrally and which of course have the xylem directed inwards. 
(The terms dorsal and ventral are applied to the lower and upper surface of 
the leaf, respectively.) 
In the simpler types of petiole the bundles are six in number, so that 
the ventral and one of the five dorsal bundles lie in the median plane, and 
Fig. 1. Vascular supply of petiole in Polygonum multijlorum . The bundles passing to the 
ochrea have been omitted. 
the other four are arranged symmetrically with regard to these. (The 
pair of bundles which occupy the upper angles of the petiole are frequently 
reduced. ) 
In the more complex forms the arrangement is the same, but owing to 
subdivision the bundles are more numerous. 
It is opposite the dorsal median bundle that the nectary is situated 
(Text-fig. 1). 
Around the nectary the tissue is somewhat raised, and may even 
slightly overhang, especially at the upper edge. For convenience of 
description this will be termed the lip. 
The nectaries are fully developed and function before the leaf unfolds : 
large drops of secretion were observed upon nectaries of P. cuspidatum 
when the lamina was not quite 2 mm. in length. 
