136 Guayule. 



DESCRIPTION OF PLATE 26. 



1. Hypocotyl of an etiolated seedling: the stele, showing rupture of wood col- 



umn and secondary opening of medullary rays. 



2-4. Sectors of the hadrome to show relative amount of conductive and mechanical 

 tissue. 



2. Field seedling. 



3. Etiolated seedling. 



4. Irrigated seedling of slow growth. 



5-7. The mechanical tissue (libriform) of hadrome of above. 



5. Field seedling. 



6. Etiolated seedling. 



7. Irrigated seedling. 



S-io. Stereome (leptome) of above. 



8. Field seedling. 



9. Etiolated seedling. 



10. Irrigated seedling. 



1 1 . Protohadrome of a field seedling ; the size of the lacunae. 



12. Same; base of a peduncle, irrigated 



13. Same; an irrigated plant, 2 cm. from apex. 



