THE FLOWERING PROCESS 



Figure 1-1 



In order to show the basic response of a number of species to day-length, 

 seeds were planted in the spring of 1962 by Mohamed N. K. El Sayed of 

 the advanced plant physiology class at Colorado State University, and 

 half of the plants of each species were placed under a light-proof box 

 every day at approximately 4.00 p.m. and removed the following mor- 

 ning around 8.00 a.m., while the remaining plants were left under the 

 long-day conditions of our cocklebur greenhouse (about 20 hr of light- 

 see Chapter 5). At various times after planting, as indicated by figures in 

 each picture, the plants were photographed. Scientific names are given 

 in the appendix. Figure A is an example of a day-neutral plant; Figs B 

 to F are absolute short-day plants ; Fig. G is nearly an absolute short-day 

 plant, although flowers can also be seen under long-day conditions 

 occasionally; Fig. H is at best only a quantitative short-day plant (see 

 Chapter 2), since it flowers on both long and short days, but faster on 

 short days; and Figs. I to L are absolute long-day plants. Note in most 

 photographs the strong eff"ects of day-length upon vegetative growth as 

 well as flowering. In many cases, exposure of the plants to the day- 

 length which causes flowering from the time they first emerge as seedlings 

 produces flowers on such small plants that the resulting examples are not 

 very typical of flowering plants in nature (e.g. Figs. B, C, D, F, and K). 

 Thus in Figs. E and I, plants were held under non-inductive conditions 

 for a few weeks before they were induced to flower. 



