530 



WEED FLORA OF IOWA 



this layer are elongated, resembling the tube-cells of cereals; but 

 short cells of more irregular shape also occur, particularly near 

 the base and apex. These are more or less separated from each 

 other, but in no part do they form a spongy parenchyma with 

 circular intercellular spaces like that of buckwheat. 3. Inner 

 Epidermis (ie). This coat consists of thin-walled, elongated ele- 

 ments. 



Pig. 407A Fig. 407B 



Fig. 407. Black Bindweed. A. Eploarp in surface view. X 160. 

 B. Tangential section of the epicarp. 

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



Endosperm (B). — None of the elements are distinguishable from 

 those of buckwheat, either in form or size. 1. Aleurone Cells (al) 

 are of variable size and irregular shape. 2. Starch-Cells {s). In 

 the outer layers the cells are tangentially elongated; farther in- 

 ward, they are radially elongated and of large size. The polygonal 

 or rounded granules vary in diameter from 0.003 to 0.012 mm. 

 Vogl has noted that after treating the starch aggregates of buck- 

 wheat with caustic potash, there remains a network corresponding 

 to the outline of the starch granules, the threads of which are of 

 homogeneous structure without granules. This phenomenon I have 

 also observed in the fruits of P. convolvulus and other species of 

 Polygonum as well as in a number of species of Rumex, and it is 

 probably characteristic of the entire family. The Embryo, con- 

 sisting of an elongated radicle and two oblong cotyledons, may be 

 conveniently isolated by soaking the seed in 1.25 per cent, caustia 

 soda solution for some hours until the starch is removed. 



