B. ESTHER STRUCKMEYER 169 



ticularly those next to the phloem which were probably phloem paren- 

 chyma cells and perlcycle cells. Thirty-two days after treatment roots 

 developed from the phloem side of the vascular bundle were emerging 

 through the cortex and epidermis (Fig. 3, 4). 



Ninety-six hours after treatment proliferation of cells was apparent 

 in the interfasicular region of the second internode from the stem tip 

 of cocklebur. Only a few scattered cell divisions were apparent in the 

 cortex (Fig. 5). Twenty-five days after treatment roots had extended 

 beyond the cortex (Fig. 6). Unlike tomato, where proliferation occurred 

 anywhere in the cambium of the stem, lateral roots were formed only 

 from the interfasicular region of the stem of cocklebur. This resulted 

 in a misplacement of the vascular bundles in the stem perhaps due to 

 the pressure of the developing roots extending through the cortex. 

 The leaves and stem tips of cocklebur were also studied. The stem tip 

 had enlarged to several times its normal size, the apex being broader 

 and the surrounding leaves showing masses of proliferating cells (Fig. 

 8, 9). Prohferating cells forming root primordia gave rise to the swellings 

 of the veins and midrib of the leaves (Fig. 7). 



Coleus responded to 2,4-D in that large root primordia were formed 

 from the fasicular region of the stele. The cambium, phloem parenchyma, 

 and ray cells proliferated to form root primordia (Fig. 10, 1 1). Poinsettia 

 also gave a marked response to 2,4-D, which appeared later than in the 

 above species. Other species such as sweet potato, Oxalis, lambs'- 



LEGEND FOR FIGURES 14 TO 23 



Figure 14. Cross section from normal plant of Tradescantia. Figure 15. 

 Cross section of stem of Tradescantia after treatment with 2,4-D; lateral roots 

 appear to differentiate from the meristematic zone near the periphery of the 

 stem. Figuie 16. Cross section of normal stem of Philodendron. Figure 17. 

 Cross section oi Philodendron stem which failed to respond to 2,4-D. Figure 18. 

 Cross section of normal quack-grass rhizome. Figure 19. Rhizome of quack 

 grass treated with 2,4-D. Band of lateral roots encircled rhizome which 

 differentiated from meristematic zone. Figure 20. Fourth internode of cockle- 

 bur grown at a temperature of 7o°C. with complete nutrient solution. Figure 

 21. Fourth internode of cocklebur grown with nutrient lacking calcium. 

 Figure 22. Fourth internode of cocklebur grown in a nutrient lacking calcium 

 but treated with a-naphthaleneacetamide. Figure 23. Fourth internode of 

 cocklebur grown with a complete nutrient supply and treated with a-naph- 

 thaleneacetamide. 



