156 Guayule. 



DESCRIPTION OF PLATE 36. 



1. Transverse section, lower end of a tap-root after considerable secondary thick- 



ening, to show large size of primary canals. 



2. Same, diarch secondary root. 



3. Detail, to show thin secondary cortex and secondary canals. 



4. Triarch secondary root. 



5. Stem of slow growth. The large size of the cortical canals is notable. 



6. Diagram of the medullary canals at the apex of a slowly growing stem. 



7. Early anastomosis of primary cortical canals, parallel to the plane of the 



cotyledons. 



8. Same, at right angles to the plane of the cotyledons. 



