LVL— THE AMPHIBIOUS PERSICARIA. 
Polygonum amphibium Linne. 
T HE genus Polygonum , which gives a name to a Sub-Family, a Family, and an 
Order, is itself appropriately named from the many “ knees ” or bent and 
swollen nodes in the stems of many of its hundred and fifty species, from the Greek 
7roXu5, polus, many ; yoov, gonu, knee. The same character is the origin of the 
English name Knot-grass , which is borne by many species, the German Kn'dterich. 
Although all the species are herbaceous, they exhibit a great variety in the 
adaptations of their vegetative structures to many different conditions of life. In 
Northern Asia there are several large rapidly-growing forms, the stout aerial stems 
of which, with taper-pointed leaves and foamy masses of cream-white blossoms, are 
now familiar objects in our shrubberies. P. baldschuanicum Regel is an attractive climber, 
with slender quick-growing stems, heart-shaped leaves, and a profusion of flowers. 
Other species are xerophytic, and others again more or less completely aquatic. 
Some of them are polymorphic, as are our Common Knot-grass (/*. aviculare Linne) 
and P. amphibium Linne, adapting themselves temporarily to varying conditions but 
often resuming their earlier form if these conditions are reversed. In some, nectar 
is secreted by the flowers, and they are mainly dependent upon insects for 
pollination : others are homogamous and at least sometimes self-pollinating. Others 
again rarely ripen their seed, multiplying vegetatively ; or produce cleistogamic flowers 
that do not open ; or bear bulbils in lieu of blossoms. 
The leaves in all are scattered and have tubular odireate stipules, while a 
resemblance in form shown by the leaves of some species to those of the Peach has 
earned for the group the name Persicaria. 
The flowers are individually small, and may be solitary in the leaf-axils or in 
cymose clusters arranged in spikes or much-branched panicles. They are mostly 
perfect and have a white or pink acyclic perianth of five united persistent leaves, of 
which the three outermost sometimes enlarge in the fruiting stage. The stamens 
also form a spiral series, five, six, seven or, most commonly, eight in number, with 
very short, subulate filaments and roundish, versatile anthers. The four outer 
stamens in the spiral probably represent branched forms, so that the number is really 
the same as that of the perianth-leaves. The superior ovary may be compressed or 
three-sided, but is not winged, and the entomophilous character is reflected in the 
simple capitate or knob-like stigmas which terminate the two or three stigmas. The 
brown and generally polished seeds contain a mealy albumen which forms the 
valuable portion of the nearly allied Buckwheat ( Fagopyrum esculentum Mcench), the 
Ble Sarrasin of the French, so-called because introduced either by the Crusaders or 
by the Moors in Spain. 
The Amphibious Persicaria ( P . amphibium Linne), a native of North Temperate 
and Arctic regions, is a striking plant and exhibits a two-fold dimorphism, both in 
