FLOWERING HORMONE MOVEMENT AND ACTION 199 



the flowers will ultimately produce an embryo which is not in the 

 induced state, a cytoplasmic change might seem more likely than a 

 nuclear one. Yet the observation mentioned in the above section 

 (that stability of the flowering hormone and hence the induced state 

 probably depends upon the presence of actively dividing cells) might 

 indicate the converse: the induced state is a condition of the nuclei 

 of the meristems, caused by flowering hormone. Is this condition 

 then reversed by formation of the gametes at miosis ? At any rate 

 it is easy to imagine that the change during vernalization is very 

 similar. Is the change during maturation also similar? This could 

 be a fruitful field for future investigation. 



3. The Morphology of Transformation 



It is somewhat surprising to learn that the morphological events 

 taking place during transformation of the meristem have been 

 observed only in a very limited number of investigations. The time 

 of change from the vegetative to the reproductive form of growth 

 can be pin-pointed almost within minutes and should provide an 

 excellent subject for histological study of morphogenesis. There is 

 a considerable background of information about the structure of 

 plant meristems and the techniques required to study them. In 

 recent years the field of histochemistry has developed rapidly so that 

 it should be possible to study, in a preliminary way at least, the 

 fundamental biochemistry of transforming cells at the meristem. 



Figure 10-6 was drawn from photographs taken by W. F. Millington 

 and E. L. Fisk at Wisconsin, and by Ralph Wetmore and his 

 co-workers at Harvard University. Their study is the kind which 

 should be done in considerable detail by many scientists around the 

 world using many species until we at least have an accurate and 

 complete descriptive idea of what goes on during floral diff"erentiation. 

 Wetmore summarized the sequence of events under the following 

 five points: (1) The cells just below the "central zone" in the apical 

 meristem were the first to become active in the diff"erentiating bud. 

 This activity consisted of cell divisions and some enlargement and 

 was found in all species studied, as well as in the literature examined. 

 This could be an important finding. Perhaps research eff*orts should 

 be directed towards biochemical understanding of this phenomenon. 

 (2) Activity then spread to the other cells, including those in the 

 central zone. Cells in this zone became smaller by dividing, and 



