LIST OF PLATES. 



Facing 

 page. 

 PLATE i. A. Guayule field with all plants above 40 cm. removed, "j 



Lomas of Sierra Zuluaga > Frontispiece 



B. Guayule field of maximum density, near Apizolaya J 



2. A. The type specimen of Parthenium argentatum Gray \ 



B. Transverse section of a very old stem f 



3. A. Upper floor in a guayule factory from which pebble-mills are 



charged 



B. Lower floor: discharge chutes and ditch from pebble-mills ..... 



C. A battery of washing and sheeting machines j 



4. A. Stacks of guayule in bales. Continental-Mexican Rubber Com- ] 



pany 's factory j 



B. Experimental ground, with plants two years old from stocks. \ 

 Cedros J 



5. A. Station 2, Quadrats 5 and 6. Lomas of Sierra Zuluaga ) 



B. Station 3, Quadrat i, near Cedros. A good stand of mature \ 24 

 plants J 



6. Plants from Quadrats 5 and 6, Station 2 24 



7. A. Quadrats (Station 12) with very dense growth. Apizolaya. . . \ 



B . The same, the guayule removed J 3 



8. A. Narrow type of guayule \ , 



B. Spreading type of guayule / > 



9. A. The root-system of guayule | 



B. Groups of plants which started as retonos > 48 



C. A strongly monopodial retono ) 



10. An exceptionally tall (130 cm.) individual. Caopas 52 



11. A. A widely spreading (130 cm.) plant of guayule ) 



B. A large plant of the usual habit. Apizolaya / 



12. A biotype of guayule. The winter condition on the left 52 



13. A-C. Seedlings of typical and atypical guayule \ 6 



D. Seedlings and mature plants of these biotypes J 



14. A. An irrigated plant, from a small stock, at the height of flowering \ , 

 B. "Hembra" (on the left) and "macho" (on the right) guayule. J 



15. A. Induced retonos on a tap-root. One season's growth \ , 



B. Induced retonos on a lateral root. One season's growth / 



16. A-C. New growths after pollarding \ fi8 



D. Seedlings in limestone soil; E, in "garden" soil / 



17. A. Minimum, average, and maximum seedlings. (Station 2, quad-) 



rat 4) [ 68 



B. Irrigated plant, two years old from a stock. Cedros J 



1 8. Seedlings growing in different soils 72 



19. Seedlings growing in different soils 72 



20. A. (i) Root-cutting; (2-4) sectorial root-stem cuttings (Exp. 146). 1 

 B. Seedlings grown in different soils / 



21. A. A branch, one year's growth under irrigation ) ,, 



B. A branch in the height of flowering, second season J 4 



22. Anatomical and histological details, figs. 



23. Anatomical and histological details, figs. 



24. Anatomical and histological details, figs. 



25. Anatomical and histological details, figs. 



26. Anatomical and histological details, figs. 



27. Anatomical and histological details, figs. 



28. Anatomical and histological details, figs. 



29. Anatomical and histological details, figs. 



30. Anatomical and histological details, figs. 



3 1 . Anatomical and histological details, figs. 



to 16 128 



to 9 130 



to 13 132 



to 10 134 



to 13 136 



to 10 138 



to 5 140 



to 6 142 



to ii 144 



to 14 146 



vii 



