MICROSCOPIC STRUCTURE OP WEED SEEDS 553 



Common Vetch (Vicia sativa L.). 



This species has been studied by Harz, Tschirch and Oesterle, 

 Beck, and Sempolowski. Testa irregular, with small projections, 

 126m thick. Endosperm reduced to a single layer. The presence 

 of endosperm has been indicated by the above writers. Beck 

 speaks of an aleurone spot (Aleurone fleck) in the epidermal cells 

 of the cotyledons of this and other species of the genus Vicia. 



Malpighian. — Cells 72-75/* long, pointed at the upper end; 

 cuticle very irregular because of the projections ; cuticularized 

 layer most prominent in the depressions; pores project into the 

 walls below the light line, and partly connect with the cell cavity ; 

 the upper part of the cell is not pigmented, or very little. The 

 light line occurs just above the pigmented part of the cell. Cell 

 cavity is large at the base, narrows upward, becoming much con- 

 stricted below the light line, and above widens again. Small 

 lateral projections or pores extend into the wall at right angles to 

 the cavity. A large chromatophore, some pigment, and small 

 granules occur in the cavity. The walls in lower part of cell are 

 colored bluish brown. 



Osteosclerid. — Cells are thick-walled, 13-16. 8m long, longitudinally 

 striated. Upper and lower cross-bars nearly equal ; the inter- 

 cellular spaces elongated. Tschirch and Oesterle state that this 

 layer is not very strongly developed, but in specimens which I 

 have examined it is well developed. These cells are more or less 

 variable, as indicated by Harz, who states that they are from 

 11-13m long. 



Nutrient. — This layer is differentiated into two parts; the upper 

 consists of thin-walled, elongated cells with a yellowish pigment; 

 the cells of the lower part are larger, thin-walled and elongated, 

 containing a brown pigment. 



Nucellus. — This consists of a narrow zone of compressed cells. 



Endosperm. — Occurs in the form of thick-walled elongated cells 

 with a narrow cell cavity. Usually only one or two rows of cells. 



Embryo. — The outer row of cells of the cotyledon is continuous. 

 The exterior walls are thickened; cells below are more loosely ar- 

 ranged; small intercellular spaces in the angles of the cells; the 

 epidermal cells contain fat and protein, the others in addition an 

 abundance of spherical or elliptical starch grains measuring 25 

 x22.5m to 50x25m. Palisade cells wanting. 



