THE BUCKWHEAT FAMILY 47 



ALLIED SPECIES. The seeds of the following allied species 

 occur in commercial seeds: 



Knotweed or Doorweed (Polygonum aviculare L.) accompan- 

 ies civilized man everywhere. It is found along roads and trails, 

 forming mats of spreading wiry, jointed stems, with a leaf, a 

 pair of silvery scales and a small cluster of flowers at each joint; 

 each flower producing a slender, reddish-brown, triangular seed, 

 1/12 of an inch long. 



Knotweed or Doorweed may be eradicated from lawns by 

 repeated raking and close cutting. In the autumn the trodden 

 soil may be loosened, without inverting it, to the depth of a dig- 

 ging fork. This should be followed in early spring by an ap- 

 plication of well-rotted manure and a thick seeding of grass, 

 including some of the coarser and more vigorous growing, though 

 short-lived, species, such as perennial rye grass. A liberal ap- 

 plication of salt on gravel walks will kill it. 



Pale or Dockleaved Persicary (Polygonum lapathifoliwn L.). 

 A common, tall-growing and rather aggressive weed among grain 

 and clover on rich low land in all parts of eastern Canada. The 

 seed (Plate 72, fig. 9) is 1/10 of an inch long, more roundly heart- 

 shaped, chocolate brown, hollowed on both sides and never 

 triangular. 



Glandular Persicary (Polygonum pennsylvanicum L.). A 

 larger seed (1/8 inch), sometimes triangular, blackish, closely 

 resembling both of the preceding but more frequently bearing 

 the remainder of the upper part of the pistil at the tip. 



The evil results from permitting coarse-growing herbaceous 

 weeds to thrive in nooks about farmyards, gardens, fences and 

 other waste places arise mainly from the fact that these succu- 

 lent plants are a breeding ground in summer, and a harbour 

 during winter, for insect and fungus pests. Fences and waste 

 places are evils that should be reduced to a minimum. Where 

 it is not possible to eliminate them, the land should be made as 

 clean as possible, seeded with vigorous growing grasses, and the 

 weeds kept closely cut until the grass has full possession of the 

 soil. 



