MICROSCOPIC STRUCTURE OF WEED SEEDS 569 



Buffalo Bur or Spiny Nightshade {SoUmum rostraium Dunal). 



The black seeds are irregular on the surface, which is mucil- 

 aginous; the underlying layer consists of thijk-waJled cells with 

 large cavities into which thickened processes extend; the third 

 layer is also pigmented and consists of squarish cells or elongated, 

 compressed elements. The endosperm is composed of thick-waUed 

 cells, the outer nearly square, the others elongated. Starch ab- 

 sent; protein present. The cells of the embryo are smaller, thin- 

 walled and contain protein and fat. 



Black Nightshade {SomMJtm, nigrum L.). 



The surface of the yellowish seeds is slightly irregular. The 

 superficial layers consist of mucilaginous, parenchyma cells, fol- 

 lowed by large parenchyma cells with thickened folds. These cells 

 are, however, variable as to structure and are sometimes short 

 with folds not evident. The elongated, thick-walled portion of 

 the testa contains the yellowish pigment. The cell cavity is tri- 

 angular. The second layer of parenchyma cells is compressed. 



Jimson Weed {Datura stramonium L.). 



The blackish seeds are rough, surface irregular, cells and walls 

 of epidermis ep thick; the underlying thinner-walled cells p are 

 small, longer than broad, followed by an indistinct layer p\ whose 

 walls are not clearly defined. The layer adjacent to the endosperm 

 consists of somewhat larger cells also thin-walled. The endosperm 

 cells e are large, containing protein. 



Ground Cherry {Physalis puhescens L.). 



The epidermal cells are thick-walled, the outer walls colorless. 

 These cells contain the pigment. The parenchyma cells of the 

 second layer are elongated; an indistinct compressed layer follows. 

 The outer row of the endosperm cells are smaller, containing 

 protein. 



A discussion of the seed coats of this family is to be found in Harz, Somen- 

 liunde, 2 996-1025. 



