12 MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE, 
THE ANATOMY OF THE STEM OF POLYGONUM. 
The genus Polygonum is made up of a number of natural groups of plants which are 
closely related from a morphological standpoint. These groups or subgenera, as they are 
now technically called, each include a number of species which agree with each other in 
habit and appearance, and although thus clearly separated from one another, they mor- 
phologically form a distinct and natural genus. 
Polygonum as represented throughout the world is divided into eleven subgenera. 
Nine of these occur in America, and eight, namely, Bistorta, Aconogonon, Persicaria, 
Tovara, Avicularia, Duravia, Tiniaria and Echinocaulon are indigenous. Although there 
is more or less variation as regards the separate elements of these sections, the sections as 
a whole show marked characteristics, especially in habit and habitat. 
Bistorta and Aconogonon are either alpine or sub-alpine and grow erect. Two other 
sections, Persicaria and Toyara, are never normally alpine, they prefer and flourish best 
in damp situations, their position is usually erect and their aspect not dissimilar. Sec- 
tions Avicularia and Duravia thrive best, as a rule, in dry places, while Tiniaria is 
scandent by its twining stems, and Echinocaulon reclines on surrounding objects and 
often climbs by means of recurved prickles. 
These general variations in habit and habitat suggested a comparative study of the 
stems of the eight indigenous sections. For this purpose a type has been selected from 
each, in most cases the type species, if it is native in America; otherwise a near relative 
was taken. For Bistorta, Polygonwm bistortoides; for Aconogonon, P. alpinum; for Per- 
sicania, P. Pennsylvanicum; for Tovaria, P. Virginianwm; for Avicularia, P. aviculare; for 
Durayia, P. Californicum; for Tiniaria, P. scandens, and for Echinocaulon, P. arifoliwm. 
The anatomy of the stem of Polygonum, as brought out by the eight examples, will 
be described below, and this general description will be followed by a detailed and com- 
parative account of the structure of each type. 
THE GENERAL ANATOMY. 
The stems under consideration are composed of three cylinders which are derived 
from the three cell-layers of the embryonic or meristematic stage. The first, that arising 
from the dermatogen layer, is the epidermis; the second, that following the epidermis and 
derived from the periblem layer, we will{designate as the periblematic cylinder, while the 
third and largest, which is produced by the plerome, forms the pleromatic cylinder. 
These cylinders, in their mature state, are well developed in all cases, clearly marked 
off from each other, and are also respectively composed of the same tissues and elements. 
