MICROSCOPIC STRUCTURE OP WEED SEEDS 



519 



The tissue is made up of irregular spongy-parenchyma cells, 

 usually transversely elongated with large, round or elongated inter- 

 cellular spaces. 



The Testa (S). — Consists of one layer of elongated brown cells 

 10-20A wide. 



Perisperm (N). — This layer is enormously developed. As may be 

 seen in cross section, the cells are 40^ thick, but the walls are so 

 swollen as to almost entirely obliterate the oavity. After soaking 

 for some time in 1 per cent soda solution they are evident in sur- 

 face view. 



Endosperm. — 1. The Aleurone Layer (al) is not of especial in- 

 terest. 2. The Starch-Parenchyma (st) is remarkable for the thick- 

 ness of the cell walls (often 10/* thick) and the elliptical starch 

 grains 3-20/* in diameter. With proper illumination each grain 

 may be seen to have an elliptical hilum. 

 ep 



Fig. 397. Chess. 



Elements of fruit in surface view. Significance of letters same 

 as in Fig. 396. 

 (After "Winton, Conn. Agr. Exp. Sta.) 



Wild Barley or Squirrel-tail Grass {Hordeum juhatum L.). 



The grain is adherent to the palet. The epidermis consists of 

 thick-walled, tangentially elongated cells, most of which are longer 

 than broad. In part the cells are developed into short conical 

 trichomes. The underlying cells are thick-walled with prominent 

 pore canals. The remainder of the adhering palet consists of thin- 

 walled cells much larger than broad. The pericarp as well as the 



