PLATE 20 



A. — Cross section of the tip of a very young cob. X 300. 



B. — Portion of a cross section of a young cob just back of the tip, showing the rudi- 

 ment or primordium from which a pair of spikelets will develop. X 300. 



C. — Cross section of a rudiment at the beginning of its division into equal parts. 



X 300- 

 D. — Cross section of a pair of spikelets in the process of development. X 300. 



