MICROSCOPIC STRUCTURE OF WEED SEEDS 549 



Bur Clover (Medicago denticulata Willd.). 



The seeds of this species agree with those of M. lupulina. 



Malpighian cells 35-38-" long; the narrow light line occurs be- 

 low the conical layer; the chromatophores are absent. 



Osteosclerids 16-18** long; longitudinal striae well marked. 

 Cross sections show beyond a doubt that these striae are canals. 

 The nutrient layer is much compressed. 



Aleurone layer of endosperm as in M. lupulina. The mucil- 

 aginous reserve cellulose not so strongly developed as in the last 

 species. Treatment with iodine gives no reaction for starch ; nor 

 do blue grains appear when treated with weak sulphuric acid and 

 iodine, or potash and iodine. An abundance of fat and protein 

 grains occurs in the cells. "Walls of the reserve cellulose color 

 light blue. Malpighian cells a darker blue. 



Sweet Clover (Melilotus alba Lam.). 



Testa and endosperm vary in thickness, average 75a*. Malpighian 

 cells as long as the thickness of the endosperm and remainder of 

 testa. 



Malpighian. — Cuticle wavy and well developed ; the cuticularized 

 layer below with small, conical projections, those of two adjoining 

 cells meeting at the middle lamella of the lateral walls, giving the 

 layer the appearance of consisting of conelike projections. These 

 cones are also connected with the small pore-canals. This cuticular- 

 ized layer is highly refractive. The light line consists of a nar- 

 row but distinct refractive zone below the conical layer. The 

 refractive zone colors blue with chlor-iodide of zinc. The whole 

 upper part is more or less refractive. The remainder of the cell 

 wall contains pigment and is colored blue with chlor-iodide of 

 zinc; the cuticularized layer as well as the conical layer colors 

 blue. Small canals project into the walls, and in some cases extend 

 beyond the light line. The chromatophores are irregularly dis- 

 tributed in the cell cavity, some near the base, others in the center. 



Osteosclerid. — Cells with a broad base and a small triangular 

 intercellular space above ; longitudinal pore-canals in the upper 

 part of the cell, but these do not extend its entire length. 



Nutrient. — This layer is much compressed; consists of thin- 

 walled cells, divided into two parts; cell walls of lower part 

 thicker. Both layers contain pigment and tannin, the upper more 

 than the lower. Cell walls consist of cellulose. 



