78 



THE FLOWERING PROCESS 



LEAF NUMBER 

 Figure 5-4 

 Length of the leaf midrib and flowering as a function of leaf number. 

 The smallest leaf longer than 1 cm is considered to be number 1, the 

 next largest number 2, etc. Experiments were performed in the fall of 

 1953 in Pasadena, Cahfornia. See F. B. Salisbury, 1955, Plant Physiol. 

 30, 327-334. 



almost exclusively. Plants are sorted with the help of a plastic 

 measuring device, and the No. 2 leaf is removed along with all of 

 those below the No. 3 leaf. We sort for No. 3 leaves which are 5.9 

 to 7.7 cm long (small), 7.7 to 9.2 cm long (large), or 6.9 to 8.5 cm 

 long (typical). Since the No. 1 leaf is not sensitive, we usually leave 

 it on the plant. Plants are normally trimmed one day before the 

 experiment so that they can photosynthesize for one day without 

 being shaded or disturbed. Sometimes plants seem to grow according 

 to a curve different from that shown in Fig. 5-4. In such cases the 

 No. 3 leaf as defined by our measurements may not be the most 

 sensitive, but we use it anyway merely as standard procedure. If the 

 No. 1 leaf appears large enough to be sensitive, we may remove it. 



2. Arrangement of Plants on the Bench 



Plants are first arranged on the bench so that all those of one kind 

 are together. For example, all of the tallest or oldest plants may be 



