Genus Polygonum . 235 
might perhaps prevent any small insect that had been attracted by the 
nectar from climbing the stem further. 
Sphaerocrystals of calcium oxalate are generally distributed throughout 
the plant, and are always relatively crowded in the young organs and beneath 
the nectaries. 
The blades, besides possessing mucilage-secreting glands, have cells 
which appear to contain mucilage scattered at intervals in the epidermis. 
Polygonum compaction. 
In this species the nectary is an oblong, almost rectangular, shallow, 
flattened depression. It measures about 1 X075 mm. (PI. XVI, Fig. 11). 
The glandular heads of the trichomes show both radial and tangential 
subdivision, and the stalk cells also divide. The basal cells seldom appear 
to do so, and exhibit a tangentially extended appearance. 
In this species the sclerotic sheath around the stele of the stem is 
discontinuous ; it only accompanies the median dorsal bundle of the 
petiole as slight sclerotic strands on either flank, the epithem tissue there- 
fore abuts direct upon the phloem. 
It consists of 2-3 layers of cells with dense contents and sclerized 
walls which are pitted. The lip does not overhang but has a well-developed 
and strongly thickened epidermis of radially elongated cells. 
The petiole is roughly rectangular with rounded corners and with 
three ridges on the upper surface (PI. XVI, Fig. 7). Its vascular supply is 
somewhat more complex than in the previous species. It consists of twelve 
bundles— two of which, situated in the lateral ridges, are small, and two other 
small ones occur one on either side of the median dorsal strand. Here 
again, calcium oxalate crystals are numerous beneath the nectary. 
Polygonum sachalinense. 
This species, which is by far the largest of those investigated, has 
a much more complex petiole structure (PI. XVI, Fig. 6). 
In transverse section as many as nineteen or twenty bundles may 
be present. Associated with this large size and consequent increase of 
vascular supply we find an augmented system of extra-floral nectaries ; 
a large one about 2x1 mm. upon the abaxial face of the leaf-cushion, and 
from 2-4 paired nectaries of ellipsoid form situated above the main lateral 
veins of the leaf-base, at the points where they emerge from the stem. 
All these glands are present on the youngest leaves. The accessory glands 
measure about 0-25 x 0-75 mm., and except in point of size their structure 
agrees with the main nectary. The latter is sunk about a millimetre below the 
surface, and is an almost flat depression (PI. XVI, Fig. 4). The basal cells 
are separated from the phloem of the underlying bundles by from 3-4 
layers of cells which are strongly sclerized and deeply pitted (Text-fig. 6), 
