MICROSCOPIC STRUCTURE OP WEED SEEDS 547 



Malpiffhian. — Cells 40-42/* in length. Cuticle slightly irregular; 

 underneath the cuticle a light colored area with conical projec- 

 tions, as in Melilotus, but somewhat more prominent. "With chlor- 

 iodide of zinc this rapidly colors blue. It corresponds to the 

 mucilaginous "membrana interna" of Mattirolo and Busealioni, 

 and, as shown by Schips, is chemically differentiated from the 

 cuticle and remainder of the cell wall. The conical layer is highly 

 refractive. The light line occurs below the conical layer and colors 

 blue soon aftpr the addition of chlor-iodide of zinc. The cell cavity 

 is broadest kt the base, gradually tapering upward. A large 

 chromatophore occurs at the base or near the middle of the cell 

 cavity. In colored seed some pigment occurs in the cavity as well 

 as considerable amounts in the walls. Small pore-canals occur in 

 the upper part of the cell wall. The cell walls color blue more 

 slowly with chlor-iodide. of zinc than the cuticularized layer. 



Osteosclerid.-^Cells broad at the base, with conspicuous longi- 

 tudinal pores; intercellular spaces below the Malpighian cells tri- 

 angular ; walls colored brownish ; cells containing pigment and 

 tannin. 



Nutrient. — This layer is much compressed, and differentiated 

 into two parts; cells elongated, rather thin-walled; those in the 

 lower portion carry a great deal of pigment, and are much more 

 compressed than the upper portion. 



Endosperm. — The endosperm is of unequal development, later- 

 ally as much as 150/* in thickness. Harz gives the thickness as 

 250/*.;; Cells of the aleurone layer rectangular, thick- walled, and 

 filled with fat and protein grains. This layer is followed by re- 

 serve cellulose. The primary wall persists when treated with weak 

 solvents. The walls, except the primary, color blue with chlor- 

 iodide of zinc. The inner portion of the endosperm consists of 

 thick-walled, elongated cells. 



Embryo. — ^CeUs of the first row smaller than those below; ex- 

 terior walls thickened more than the lateral; all of the cell walls 

 consist of cellulose. Cells contain fat and protein grains; starch 

 grains do not occur, though Harz says they are usually abundant. 

 In several specimens examined starch was not found even when 

 potassium hydrate or weak sulphuric acid was used with the iodine. 



