LIST OF PLATES. 



Facing 

 page. 



Plate i. A. Guayule field with all plants above 40 cm. removed. J 



Lomas of Sierra Zultiaga > 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 I 



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



charged I g 



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



C. A battery of washing and sheeting machines 



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



pany's factory I 



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

 Cedros J 



5. A. Station 2, Quadrats 5 and 6. Lomas of Sierra Zuluaga 1 



B. Station 3, Quadrat 1, near Cedros. A good stand of mature j- 24 

 plants ) 



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 \ o .. 



B. Spreading type of guayule J 



9. A. The root-system of guayule } 



B. Groups of plants which started as retohos j- 48 



C. A strongly monopodial retono J 



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



1. A. A widely spreading (130 cm.) plant of guayule \ 



B. A large plant of the usual habit. Apizolaya j > 



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



3. A-C. Seedlings of typical and atypical guayule \ fi 



D. Seedlings and mature plants of these biotypes J 5 



4. A. An irrigated plant, from a small stock, at the height of flowering 1 , 

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



5. A. Induced retofios on a tap-root. One season's growth \ , 



B. Induced retofios on a lateral root. One season's growth j 



6. A-C. New growths after pollarding \ fi 



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



7. A. Minimum, average, and maximum seedlings. (Station 2, quad- "| 



rat 4) \ 68 



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



8. Seedlings growing in different soils 72 



9. Seedlings growing in different soils 72 



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



B. Seedlings grown in different soils / ? 2 



A. A branch, one year's growth under irrigation \ 



B. A branch in the height of flowering, second season / "* 



22. Anatomical and histological details, figs. 1 to 16 128 



23. Anatomical and histological details, figs. 1 to 9. 130 



24. Anatomical and histological details, figs. 1 to 13 132 



25. Anatomical and histological details, figs, itoio 134 



26. Anatomical and histological details, figs. 1 to 13 136 



27. Anatomical and histological details, figs, itoio 138 



28. Anatomical and histological details, figs. 1 to 5 140 



29. Anatomical and histological details, figs. 1 to 6 142 



30. Anatomical and histological details, figs. 1 to 1 1 144 



31. Anatomical and histological details, figs. 1 to 14 146 



vii 



21. 



