150 Guayule. 



Description of Plate $7,. 



i. Annual rings in duramen of an old stem. 



2. Annual rings in the wood of an 8-year-old stem. 



3-4. Parenchyma rays as seen in a tangential section of a stem of a field plant. 



5-6. Same, irrigated plant. 



7. Sclerosed parenchyma-ray cells of an irrigated plant. 



8. Tracheidal parenchyma-ray cell of a field plant. 



9. Libriform of an irrigated plant; old wood. 

 10. Same, field plant; old wood. 



