164 WEEDS OF THE FARM AND GARDEN 



Sheep Sorrel (Rumex acetosella, L.). Sheep sorrel is 

 closely allied to the docks and is quite prevalent in many 

 parts of the North. It is a low, smooth annual or peren- 

 nial, usually the latter, growing from six to twelve 

 inches tall, and coming from a horizontal, creeping root ; 

 stem erect; leaves narrow, eared, lanceolate (the upper 

 linear) ; flowers terminate, jointed stalks or stems, and 

 are small, with green calyx and exserted stamens. Com- 

 mon in pastures and clover fields, the seed being some- 

 times introduced as an impurity in clover seed. The 

 plant is also spread by means of underground roots and 

 stems. 



There is a widely spread belief that the soil in which 

 this plant occurs is sour, that is, is lacking in lime, and 

 that the addition of lime will exterminate the weed; but 

 this opinion is erroneous, since sheep sorrel is quite as 

 common upon the calcareous soils of Wisconsin and 

 eastern Minnesota as it is on the dry, sterile hills of 

 Massachusetts and Iowa. 



Knotweed or Dooryard Weed (Polygonum aviculare, 

 L.). A slender annual, or more commonly, a perennial, 

 with a prostrate or somewhat ascending stem from six to 

 twelve inches long; leaves ovate, lanceolate or oblanceo- 

 late with a short petiole, smooth or sparingly hairy; 

 stipules, called ochrese, silvery, two-parted, later cut or 

 fringed ; flowers in axillary racemes from one to five ; 

 sepals green with five lobes ; style short, three divided ; 

 achene striated, three-angled. A common weed through- 

 out eastern North America to the Pacific coast. Intro- 

 duced from Europe. Found in both Europe and Asia. 



Related to P. aviculare, is the larger knotweed (P. 

 erectum), a glabrous annual, with erect stem fronv eight 

 to fourteen inches high ; leaves oval or oblong, nearly ses- 

 sile on short petioles ; flowers one to two in the axils of 

 the leaves; stamens six, occasionally five; style short; 

 achene three-angled. Native from New England to On- 



