140 Guayule. 



DESCRIPTION OF PLATE 28. 



1. Irrigated plant, stem i year's growth. 



2. Field plant, stem 2 years' growth. Note width of parenchyma rays and depth 



of cortex. (Figs, i and 2 are drawn to same scale.) 



3 . Hypocotyl, field seedling less than i year old. 



4. Cortex of hypocotyl after secondary enlargement. Transverse section. 



5. Cortex of root; tangential section. 



