70 



THE FLOWERING PROCESS 



112 

 Nov. I 



TIME IN DAYS 



168 

 Dec.26 



Figure 4-5 



Temperature treatment for early flowering of Tulipa gesneriana " W. 

 Copland " and of Iris xiphium " Imperator ". With the tulip, flower 

 initiation begins and is well under way during the 20°C treatment. 

 Moving to 8° and then 9° provides an acceleration in blooming, so that 

 flowers are produced at Christmas. Continuous 9°C treatment gives 

 equal earliness, but quality is poor unless the 20°C treatment is given 

 first. The bulbs are planted in a controlled temperature greenhouse 

 about midway during the low-temperature treatment. The temperature 

 is first raised when the leaf tips are visible, then again when they are 3 cm 

 long, and finally again when they are 6 cm long. The low-temperature 

 optimum and the gradual change to higher optima as active growth 

 begins have been related to conversions of starch to sugar during this 

 period. Respiration rates also increase. With iris, the short period at 

 high temperature is completely essential to flowering, although actual 

 initiation of flower primordia does not occur imtil the bulbs have 

 been moved from low temperature to 15°C, at which time the sprouts 

 are about 6 cm long. Again, the 9°C treatment is to insure earliness. At 

 temperatures much above 15°C during the last part of the treatment, 

 abnormal flowers may be produced. Low light intensities will also result 

 in " blasted " flowers at this time, especially if the temperatures are not 

 right. K extremely high temperatures (38°C) are used during the first 

 flower induction period, flower parts are increased or decreased, or 

 tetramerous, pentamerous, or dimerous flowers result. Data from 

 Annie M. Hartsema (17). 



