MICROSCOPIC STRUCTURE OF WEED SEEDS 



515 



forms have exceedingly thin walls. 2. The Inner Epidermis is dis- 

 tinguished from the outer by the straight walls and almost entire 

 absence of hairs. 



Flowering Glume. — The fourth or flowering glume, situated be- 

 tween the upper or second glume and the grain, is also mem- 

 branous and bears an upwardly barbed awn 5 to 7 mm. long. This 

 awn, with the larger part of the flowering glume, being readily de- 

 tached by threshing, it is seldom found in the grain on the market. 



Fig. 393. Broom-corn. Glume of rudimentary flower in surface view, aep, 

 outer epidermis with h, one-celled hair and h, two-celled hair ; iep, inner 

 epidermis. X 300. 



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



Palet. — This is membranous and hairy like the third or thin 

 glume, but is much smaller. 



Pericarp. — The grain or caryopsis is about 5 mm. long and from 

 2 to 3 mm. wide, tapering to a blunt point at both ends. It varies 

 in color from yellow-brown to red-brown. 



Harz, Hassack and particularly Mittlacher have described so 

 fully the histological elements of the caryopsis, that only a brief 

 description, essential for a clear understanding, need here be given. 

 1. Epidermis. The cells are longitudinally extended and have 

 thick wavy side walls, with more or less distinct pores. Hassack 

 has noted that the cuticle is of uneven thickness, due to minute 

 granules or crystals, which may be seen in either section or sur- 



