THE GENERAL CHARACTERS OF SEEDS 



429 



Black Bindweed {Polygonum convolvulus L.). 



Achenes large, prominently 3-angled, ovoid-pyramidal, one- 

 eighth to one-sixteenth in. in length; surface dull, with minute 

 striae; color blackish; perianth usually removed, when present 

 straw-colored. 



Figure 263 B 



Fig. 263. A. Black Bindweed (.Polygonum convolvulus). A and B, views of 

 two seeds, the latter bearing a portion of the perianth about the base. C, 

 a view of an entire perianth covering a, seed. D, a group showing the 

 natural size. 



B. Erect Knotweed (Polygonum erectum). 



(After Hlllman, Bull. Mich. Agr. Exp. Sta.) 



Erect Knotweed {Polygonum erectum L.). 



Achenes 3-angled, ovoid, less deeply concave between the angles 

 than in preceding (P. aviculare) ; one-ninth to one-tenth in. in 

 length ; dull, minutely reticulated. 



Figure 264A Fig 264B 



Fig. 264. A. Water Pepper (Polygonum hydropiper). Seeds enlarged and 



natural size ; the embryo at C. 

 B. Mild Water Pepper (Polygonum hydropiperoides) . 



(A, after Hlllman; B, drawing by Ada Hayden.) 



