398 



GROWTH FACTORS AND FLOWERING 



Table IL Average Leaf Lengths (in mm ± Standard Error) after 68 Days and 

 Av'erage Days to Flowering of Colcits Plants Treated as Shown 



Average days to flowering 



Average days to flowering- 

 ready-to-fiower plants 



76.1 ''±1.98 (9) 



38.y ± 1.52 (9) 



" Signifies a statistically highly significant difference, by the t test, between the marked 

 average and the average for the same leaf position in the central column. 

 *" Signifies a statistically significant difference, as above. 



Excising Very Young and Old Leaves on the Main Shoot 



If, in addition to removing all axillaries, leaf pairs 1 and 2 are 

 excised and leaf pairs A, B, C, etc., are excised as soon as they have 

 unfolded from the apical bud and have reached the size of the original 

 leaf pair 1, then additional compensatory growth is induced in leaf 

 pairs 3 and 4 (Jacobs and Bullwinkel, 1953). Still greater compensa- 

 tory growth results from excising the smaller leaves of original size A 

 (ca. 15 mm) in addition to excising size 1 leaves (Jacobs and Bull- 

 winkel, 1953). In other words, the more leaves removed, the greater 

 was the growth in those leaves remaining, as one would expect from 

 the concept of compensatory growth. 



Does this statement hold for all other patterns of deblading? Further 

 experiments showed it did not. 



When the plant was completely stripped of its unfolded leaves (pairs 

 1-8), leaving only the small leaves in the apical bud (A-E), the young 

 leaves did not show as much growth as when some of the older leaves 

 were left on (Table III and Fig. 6; three repetitions). In other words, 

 this pattern was an exception to the concept of compensatory growth. 

 And, as with all the compensatory growth studied so far in Coleus, 

 lAA which was substituted for the older leaves (5 + ) had no effect on 

 the growth of the initially very young ones (Fig. 6 and Table III; also 

 Jacobs, 1955, Table 4). 



