EXPERIMENT STATION BULLETINS. 



296 



BUCKWHEAT FAMILY. POLYGONACEAE. 



Mostly herbs with entire leaves and stipules in the form of sheaths extending around the stem; 

 flowers with a calyx more or less persistent; ovary one-celled, becoming an achene -.in fruit, flat- 

 tened or 3-4- angled. Among its 800 species the family contains few of economic ^importance, ^but 

 is rather conspicuous for the weeds it affords. Here are sorrels, docks, knot weeds, smart wped.« and 

 others. 



Fig. 31 (31). 



Knot-grass. Door-weed. Polygonum 

 aviculare L. A slender, prostrate or erect 

 annual (perennial 'farther south), dull or bluish 

 green in color, usually less than 30 cm. high; 

 leaves small; flowers small, inconspicuous; fruit 

 a triangular achene, dull, minutely granular 

 and striate. Common along paths and about 

 door yards. Native to this country, Europe 

 and Asia. 



Fig. 32 (32). 



Wild Buckwheat. Black Bindweed 



Polygonum Convolvulus L. An annual, twin 

 ing or trailing vine, 10-90 cm. or more long 

 leaves heart-shaped or halberd-shaped, pointed 

 flowers greenish in slender, interrupted racemes, 

 fruit three-angled, dull, black; in cultivated 

 annual crops. Introduced from Europe. 



