Tunica 

 Corpus: 

 Central mother 

 cell zone 

 Transition zone 

 Peripheral zone 

 Rib meristem- — 



50 



100 Microns 



Figure 10-6 

 Histological changes during transition from the vegetative to the 

 reproductive condition. A. Median longitudinal section through the 

 shoot tip of a vegetative cocklebur plant. Drawn from a photograph in 

 W. F. Millington and E. L. Fisk, 1956, Amer.J. Botany 43, 655-665. 

 B. Tracing of the section in A, showing the zonation proposed by 

 Millington and Fisk. Note in A and B the large, lightly staining nuclei 

 in the tunica; the 2 rows of cells almost continuous with the tunica, also 

 having large, lightly staining nuclei (the central mother cell zone); the 

 2 to 3 rows of cells immediately below, having much denser nuclei (the 

 transition zone); and finally the rib meristem, having cells at the top 

 similar to the transition zone cells, but cells with larger vacuoles and 

 smaller nuclei below. C. Beginning the transition to the floral bud (an 



