viii List of Plates . 



Facing 

 page. 

 Plate 32. Anatomical and histological details, figs. 1 to 7 148 



33. Anatomical and histological details, figs. 1 to 10 150 



34. Anatomical and histological details, figs. 1 to 9 152 



35. Anatomical and histological details, figs. 1 to 15 154 



36. Anatomical and histological details, figs. 1 to 8 156 



37. Anatomical and histological details, figs. 1 to 8 158 



38. Anatomical and histological details, figs. 1 to 18 160 



39. Anatomical and histological details, figs. 1 to 8 162 



40. 1. Rubber in canal-cells, nearby cortex and inner ray-cells 



2. Older root. More rubber in rays 



3 . Root 2 mm. diameter 



4. Parenchyma ray from fig. 2 



5. Upper part of hypocotyl, same age as fig. 1 



6. Longitudinal section through old wood 172 



7. Longitudinal section through mature leptome parenchyma, with 



a few parenchyma-ray cells 



8. Leptome ; elongated elements 



9. Companion cells and sieve-tubes. No rubber in younger leptome 



on the left ' 



41. 1,2. Cortex, stem of field plant with maximum rubber-content. . 



3. Cortex of a 20-year-old stem 



4. Root ; rapidly grown seedling, 2 months old. Rubber in granules, j- 172 



5. Rubber in process of accumulation in an irrigated plant | 



6. Primary resin-canal J 



42. 1. Apex of terminal twig of 1908, field plant 



2 . Near base of same 



3. Pseudotylosis with rubber in the cells 



4 . Leptome, field plant 



5. Pith of a field stem 10 mm. diameter 176 



6. An old leaf-trace 



7 . Outer cortex of a field stem 



8. Outer edge of cortex and inner zone of cork derived from collen- 



chyma 



43. 1. Base of 1908 growth, August. Cedros, irrigated "| 



2. Growth of 1908 in April 1909. Cedros, irrigated j 



3. Cortex, 2 -year-old stem. Caopas, irrigated \ 192 



4. Pith of same plant I 



5. Epidermis and palisade of an old leaf, field plant J 



44. A. Irrigated plant, 2 years old. Basal branches which have rooted | 



are spread apart j- 192 



B. Mariola showing the same behavior, normal in this species. ... J 



45. A. Flat filled with paper tubes, 1 square inch in transverse section. ] 



B. Flat with 4-square-inch tubes | 



C. Exp. 141 (3), i-inch tubes; very poor growth. Exp. 143,4-inch [ 204 



tubes 



D. The same, seedlings well grown 



46. A. Seedlings from experiments indicated ) o 



B. Irrigated plant (Caopas) with a retono J 



