546 



WEED FLORA OF IOWA 



Malpighian. — The cells are prismatic in surface view, 9.8/» 

 across, with five to six canals. In cross sections they are 84^* long. 

 The cuticle forms a continuous layer, with longitudinal canals pro- 

 jecting into the cells; these extend down through the upper part 

 of the cell wall and the cuticularized substance ; this layer is lighter 

 in color than the rest of the cell wall, and separates from the re- 

 mainder of the cell in the form of a band. The narrow light line 

 occurs close under the cuticularized layer. The cell cavity is 

 narrow and gradually tapers upward; it contains some protein 

 matter. The cell waU consists of cellulose. 



Osteosclerid.— The walls are thickened. Cells wide in the lower 

 part and narrowing upwards, with large intercellular spaces. Cells 

 contain protein. 



Nutrient. — Consists of radially elongated cells, which are slightly 

 compressed. Walls of medium thickness, slightly colored. 



I ■! ■Irti:i:i:i.;i^'i:i:i'' 



Fig. 420. Microscopic structure of the testa of Rattle-box iCrotalaria aagittalis'). 

 Il=llght line.- m=malplghlan cells. n=nutrient layer. o^osteosclerld. 

 (Drawing by L. H. Pammel.) 



Endosperm. — ^Not strongly developed. The cells of the aleurone 

 layer large, containing protein. Two layers follow this, the cells 

 very much compressed, and somewhat radially elongated, of thick- 

 walled cells. All of the cells contain protein and fat. 



Embryo. — Cells of outer row smaller; those adjoining the en- 

 dosperm thicker walled, the inner part with thinner walls. The re- 

 maining cells of the embryo larger. All of the cells filled with 

 protein. Starch is absent. 



Black Medlck {Medicago lupulina L.). 



Testa and endosperm well developed, 245/* in thickness on sides. 

 More than half of this thickness consists of endosperm. 



