550 WEED FLORA OF IOWA 



Endosperm. — The aleurone layer is quite distinct; the cells are 

 rectangular; cell walls made up of cellulose. The walls of the re- 

 mainder of the endosperm, except where it joins the embryo, are 

 thick, consisting of mucilaginous reserve cellulose. Cells of the 

 internal layer of the endosperm thick-walled, elongated, containing 

 some protein grains and fat. 



Embryo. — Cells of the exterior walls of first row thickened; 

 smaller than those below. All of the cells contain fat, protein 

 grains, and small starch grains. Procambial vessels well developed. 



Yellow Sweet Clover {MeUlotus officincAis Lam.). 



Testa with endosperm varying from 260-300/* in thickness. The 

 Malpighian ceUs of this species are longer than in M. alba, and 

 also more abundantly supplied with pigment. The conical pro- 

 jections are longer. The osteosclerids are longer and nearly as 

 wide above as below. The longitudinal canals are as conspicuous 

 and well developed as in that species. Cells of the nutrient layer, 

 especially in the lower part, are abundantly supplied with pig- 

 ment and some tannin. The walls of the aleurone cells are thick; 

 the mucilaginous reserve cellulose and the thick-walled, elongated 

 cells are not essentially different from the last species. It also 

 agrees with it with respect to the embryo. 



Hairy Prairie Clover (^Dalea cdopecuroides Willd.) {Parosela 

 dalea (L.) Britt.). 



Testa and endosperm from 150-265/* in thickness. Variation is 

 mostly due to endosperm, which reaches its greatest development 

 laterally. 



Malpighian. — Cells are 36.4a' in length. Cuticle prominent; 

 cuticularized layer not conspicuous; narrow light line near the 

 cuticle; pores prominent, extending into the walls beyond the 

 light line. Cell cavity broad at the base, containing protein 

 grains. 



Osteosclerid. — Cells thick-walled, lighter in color than the Mal- 

 pighian layer. They contain pigment, tannin and protein. 



Nutrient. — This layer is compressed and the cells are elongated. 

 Walls color blue with chlor-iodide of zinc. Brown pigment 

 abundant in the vascular region. 



Endosperm,. — ^Aleurone cells nearly isodiametric, containing fat, 

 and protein; most of the endosperm consisting of reserve cellulose 



