CHAPTER III. 



GRAMINEAE,* GRASS FAMILY. 

 Smooth Crab Grass (Digit aria humifusa Pers.). 



A cross section of . seed shows but slight development of the 

 pericarp and testa. The epidermal cells of the former are smaller 

 than the underlying rows of cells of the wall of the ovary. The 

 testa is reduced to a single layer of cells, longer than broad. The 

 aleurone layer is filled with protein grains. The starch cells of 

 the endosperm are larger and densely packed with polygonal 

 grains. 



Fig. 383. Structure of the grain fruits of some Grasses (Gramineae) . 

 Wild Barley (Hordeum jubatum). II. Timothy (Phleum pratense). III. 

 Smooth Crab Grass (Digitaria humifusa). IV. Sandbur (Cenchrus tribu- 

 loides). V. Millet (Setaria italica). VI. Corn (.Zea mays). VII. Barn- 

 yard Grass (Echinochloa crusgalli) . 



t=testa. al=aleurone. en=endosperm. n=nucellus. 

 (Drawings by L. H. Pammel.) 



♦The material for this family has been taken from the accounts by Pammel 

 and Winton. 



