560 WEED FLORA OF IOWA 



brownish pigment cells of two or three rows. Adjacent to tha 

 pigment layer is the colorless compressed nucellus and the squarish 

 endosperm cells. 



Sida (Sida spinosa L\). 



The brownish seeds are minutely roughened. The Malpighian 

 cells occupy more than one-half of the thickness of the testa, the 

 cuticle is well developed, the light line occurs near the upper end 

 of the cells. The cell cavity is spindle-shaped near the lower end 

 of the cell. The subepidermal layer contains the brownish pig- 

 ment, the walls of these cells are thickened; the parenchyma cells 

 of the layer underneath are colorless, the walls are less thickened; 

 a narrow pigment layer follows. The cells of the endosperm are 

 thick-walled containing protein grains. 



ONAGRACEAE, EVENING PRIMROSE FAMILY. 



Evening Primrose {Oenothera biennis L.). 



The small, irregular, winged seeds are rough. The epidermal 

 cells, ep, of the testa are small, thick-walled with minute pore 

 canals; the underlying parenchyma cells, p, are large, thick- walled 

 and with small pore canals ; these cells reach their greatest develop- 

 ment where the wings occur. The remaining portion of the testa 

 consists of four or five layers of cells more or less rectangular. 

 The nucellus and the endosperm much compressed, outer epidermal 

 cells of the embryo, em, thin-walled, a little longer than wide. 



Fig. 427. Microscopic structure of the seed of Evening Primrose {Oenothera 



biennis). 

 ep=epidermis of thick-walled cells. p=thick-walled parenchyma underneath 

 thinner-walled parenchyma. n=nucellus and below a few layers of cells of 

 the endosperm. 



(Drawing by Charlotte M. King and L. H. Pammel.) 



