DEVELOPMENT OF VEGETATIVE AND FLORAL BUDS 267 



Figs. 15-20. Apices of Xanthium pensylvanicum during induction. 



15. Terminal apex of 2 days after three photoperiods. Compare with 

 Figs. 18, 19; note extension of cell growth into peripheral zones in region 

 of gaps of flower bud primordia. Xl50. 



16. Terminal apex 4 days after three photoperiods. Compare with 13. 

 X75. 



17. Terminal apex 6 days after three photoperiods. Note flower buds 

 forming in axils of bracts. X 100. 



18. Terminal bud 2 days after five photoperiods. X65. 



19. Terminal apex following six photoperiods. Xl50. 



20. Terminal apex 2 days after six photoperiods. x75. 



