130 Guayule. 



DESCRIPTION OF PLATE 23. 



1-7. Tap-root. 



1. Field seedling. 



2. Irrigated seedling. 



3-5. Field seedling, 2 mm. diameter (cf. plate 40, figs. 2, 3). 



3. Sector to show arrangement of tissues and distribution of rubber. 



4. Endodermis and pericambium of a root 1.2 mm. in diameter. 



5. Same, thickened and compressed ; root 1.5 mm. in diameter; globules of rubber. 



6. Region just within primary canals. Primary leptome-stereome (sj ; secondary 



leptome-stereome (s 2 ). 



7. Parenchyma ray enlarged to show globules of rubber. 



8. Epidermis of the hypocotyl, first peridermal divisions. 



9. Trichome from hypocotyl. 



