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 wall 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. 



Fig. 420. Microscopic structure of the testa of Rattle-box (Crotalaria sagittalis) . 

 ll=light line. m=malpighian cells. n = nutrient layer. o= osteosclerid. 

 (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 Medick (Medicago lupulina L.). 



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

 More than half of this thickness consists of endosperm. 



