2 39 
Genus Polygonum. 
This was most marked in P. sachalinense where the nodes of one 
young shoot were bathed in the gummy secretion which hung down in 
sticky threads. 
With a view to finding if there were any relation between vascular 
supply and secretory area, the following table was constructed. Where 
the cross-sectional area of the xylem in the petiole of each species has been 
estimated, and the area of the corresponding nectary, it will be seen that 
the value obtained by dividing the one area by the other approaches 
a constant. 
Species. 
Approx, area 
Approx, area of xylem 
n 
of nectary in). 
in petiole ( x ). 
Value ~ 
P. baldschuanicum 
0.23 sq. mm. 
0.031 sq. mm. 
7.42 
P. cilinodum 
0-30 » » 
0-030 „ „ 
10-00 
P. compactum 
o -75 » 
0.076 „ „ 
9-87 
P. Convolvulus 
0.22 „ „ 
0-025 » » 
8.80 
P. cuspidatum 
°-57 » 
0-068 „ „ 
8.51 
P. multifiorum 
0-26 „ „ 
0.028 „ „ 
9.29 
P. sachalinense 
2 -25 „ „ 
0-247 » 
9.11 
P. scandens 
0-l6 „ ,, 
0.019 „ „ 
8.42 
V. Summary and General Conclusions. 
The petiolar nectaries are in all cases surrounded by a lip which 
is raised and covered by thickened epidermal cells. 
This lip, which projects most at the upper edge (PL XVI, Fig. i, /), 
may serve to protect the gland cells and to prevent the washing out of 
the nectary by rainwater. It may possibly further serve as a protection 
for the cells beneath against the plasmolyzing action of the osmotically 
powerful secretion contained in the nectary. 
For it is these thick-walled lip cells with which the secretion is in con- 
tact. The tangential division of the epidermis of the lip which was observed 
in P. cilinodum still further supports this view. And in this connexion we 
may refer to the well-developed lip-structure described by Miss Ewart (6) 
in Ipomoea panicidcita , as here, too, the lip exhibits a tangential division 
which may have the same significance. 
A like function may be served by the suberization of the stalk cells, for 
the secretion has access to these notwithstanding the close packing of the 
glandular heads. 
The high osmotic pressures involved may further account for the 
sclerization of the epithem cells, as the deep pittings, which are fairly 
numerous upon their surfaces, allow of sufficient facility for translocation. 
It is worthy of note that a similar pitted tissue has been observed below the 
gland cells of Ipomoea paniculata (6) which, as we have seen, closely resemble 
the glands of Polygonum in other respects. M. Vuillemin (16) has also 
called attention to the pitted tissue beneath the glands of the Tamariscineae, 
