528 WEED FLORA OF IOWA 



Wild Buckwheat or Bindweed (Polygonum convolvulus L.). 



Dr. A. L. Winton describes its microscopic structure as follows: 

 Pericarp (f). — The black hulls or shells of the grain should be 

 studied in cross section and in surface preparations, the latter 

 being freed from the black coloring matter by warming on the slide 

 with caustic alkali, or better by boiling for half an hour with 

 1.25% sodium hydrate solution as in the determination of crude 

 fiber. 1. Epicarp (epi). Cross sections show that the cells are 

 about 0.10 mm. in radial diameter on the sides of the achenes and 

 are still longer at the angles. The inner wall is thin, but the outer 



Fig. 405. Black Bindweed. (Polygonum convolvulus) . Transverse section of the 

 fruit. C, calyx ; Epi, epicarp ; Mes. mesocarp ; B, fibro-vascular bundle ; S, 

 testa; E, endosperm; Em, embryo. X 16. 



(After Winton, Conn. Agr. Exp. Sta.) 



wall and the outer portions of the curiously wrinkled radial walls 

 are strongly thickened. Proceeding from the inner wall outward, 

 the radial walls increase in thickness until the much-branched cell 

 cavity is almost obliterated. On the surface are numerous warts 

 from 0.015 to 0.03 mm. in diameter, into each of which a narrow 

 branch of the cell cavity passes. Surface preparations of the 

 pericarp with the outer surface uppermost clearly show that the 

 warts are arranged in irregular longitudinal rows, also that the 

 epicarp cells at the surface are sinuous in outline, but gradually 

 approach a circular form farther inward. As may be seen in 

 preparations of the pericarp with the inner surface uppermost, 

 the contour of the inner cell walls of the epicarp is, like the 

 outer wall, sinuous in outline. 2. Hypoderm (hy) . Beneath the 

 epicarp is a layer of slightly elongated parenchyma cells somewhat 

 larger than the cells of the mesocarp. 3. Mesocarp (p.) At the 

 angles of the fruit this layer is somewhat thicker than on the 

 sides. The cells of the ground tissue are thin-walled and 

 isodiametric, those of the inner layers being more or less obliterated 



