6 LIST OF PLATES. 



Facing 

 Page. 



Plate 13- 



Root habit of Jatropha cardiophylla of which the horizontal extensions of the 



root-system were shown in plate 12 52 



Plate 14. 



Horizontal and vertical extensions of root-systems of Carnegiea gigantea, 



Covillea tridentata, and Parkinsonia microphylla 56 



Plate 15- 



(a) The anchoring roots and bases of some lateral roots of Carnegiea gigantea 

 6.8 m. high, (b) Tap root and secondary roots making up the 

 anchoring system, and the bases of some of the superficial roots 

 of a specimen of Carnegiea 1.2 m. high from same habitat as cactus 

 shown in (a), (c) Tap root and bases of laterals of Parkinsonia 

 microphylla growing near Carnegiea shown in (b) and which 



appears in plate 14 56 



Plate 16. 



(a) Covillea tridentata. Horizontal and vertical extensions of roots of this 

 plant are shown in fig. 8. (b) Covillea from flood-plain near West 

 Wash, showing the large number of slender adventitious roots 

 springing from upper portion of the main roots and long tap root 

 of which only a part appears, (c) Fouquieria splendens from 

 bajada where Covillea shown in (a) was growing. Horizontal 



extension of roots of this plant shown in fig. 8 64 



Plate 17. 



(a) Franseria deltoidea from flood-plain near West Wash, showing part 

 of tap root, (b) Lateral of the first order bearing filamentous 

 roots in groups, which, at time photograph was made, were no 

 longer functional, (c) Krameria canescens from the flood-plain 

 near West Wash, showing essential superficial placing of roots. 



(d) Lycium andersonii from near West Wash 64 



Plate 18. 



Bird's-eye view of superficial roots of Opuntia arbuscula from bajada a mile 



east of Santa Cruz, showing their fleshy character 68 



Plate 19. 



(a) Riddellia cooperi showing the large number of slender laterals arising 

 from crown of tap root, and the branching feature of the bases of 

 the laterals, (b) Riddellia from red clay soil, to iflustrate lack of 

 slender roots at crown of tap root, (c) Dasylirion texanum, with 

 root-system partly exposed, (d) Shoot and root habit of Yucca 



sp. (e) Root character of Yucca radiosa 72 



Plate 20. 



Root habit of Kceberlinia spinosa. (a) Isolated plant with prom.inent tap root. 

 (b) Several shoots arising from a single sucker which still keeps its 

 connection with parent tap root, (c) Adventitious absorption 

 roots arising from a sucker which has not formed an independent 

 tap root, (d) Secondary formation of tap root in a group with 



connecting sucker root no longer living 80 



Plate 21. 



(a) Peniocereus greggii showing fleshy main root and the most important 

 laterals, (b) Condalia spathulata. (c) Root-system of Prosopis 

 velutina partly exposed by the caving bank of the Santa Cruz. 

 The vertical distance from the ground surface to the water is 

 approximately 5 m. (d) Young plant of Prosopis. The squares 

 are centimeters, (e, f, g) Cuttings of Opuntia arbuscula (Tucson), 

 O. arbuscula (Sacaton), and O. vivipara, respectively, all grown 



under similar conditions and with a large water supply 80 



.Plate 22. 



(a) Cultures of Fouquieria splendens and of garden water-melon showing 

 differences in character and development of extreme types of 

 root-systems, (b) Shoot of Opuntia vivipara springing from a 



fleshy root 84 



Plate 23. 



Brodiaea capitata grown in adobe clay (a) and in sand (b) in plant-house cul- 

 tures. Main root of clay-grown plant curved away from source 

 of water supply 88 



