192 



THE FLOWERING PROCESS 



12 3 4 5 6 7 



MONTHS AFTER BEGINNING OF INDUCTION 



Figure 10-4 

 A schematic diagram illustrating the development of cocklebur flowers 

 and fruits under conditions of continuous induction or following the 

 minimal induction of a single dark period. Up to 3 months the curves 

 are based on the observations of Francis L. Naylor {Botan. Gaz., 

 1941, 103, 146-154). Following this time the minimal induction curve is 

 based on the familiar observation that such plants will produce ripe 

 seeds, although only after an extended period, and that the size and 

 quality of seeds is much lower than in the case of maximally induced 

 plants. It is interesting to note that in Naylor's experiment, minimally 

 induced plants produced about 10 staminate and 6 carpellate flowers per 

 plant, while maximally induced plants produced about 4 staminate and 

 12 to 13 carpellate flowers per plant. 



I wondered at one time whether the rate of development of a 

 flower bud depended upon the amount of flowering hormone 

 available for that bud or whether it depended upon the concentration 

 of flowering hormone in any given plant tissue. To find out, I 

 prepared a number of plants so that all of them had a single No. 3 

 leaf. On half of the plants, all of the buds but one were removed, 

 while on the remaining plants all of the buds were left intact. The 

 entire group was then given an inductive dark period, and 9 days 

 later all buds were examined for their flowering condition. Table 10-1 

 shows the results. The average Floral Stage was not greatly different 

 on the two sets of plants, but of course, the number of flowering buds 

 was much greater on the plants with the most available buds. This 

 seems to imply that Floral Stage or rate of floral bud development 



