i6o THE STRUCTURE OF ECONOMIC PLANTS 



primary tissues is accompanied by the formation of fascicular 

 and interfascicular cambiums which produce a continuous cyl- 

 inder of secondary tissues, and these form the only connection 



Fig. 12.6 /J, transection of portion of upper hypocotyl of older seedling showing cotyle- 

 donary bundle and those of first and second foliage leaves; B, same axis at slightly higher 

 level showing further differentiation of leaf bundles : iu /-i, bundle of first foliage leaf ca 

 cambium; ca x secondary cambium; en, endodermis; wx, metaxylem ; W pericycle' p/j 

 phloem; />/, pith; ;,.v,protoxylem; xj 2., secondary xylem. (After Lyle ) 



