402 GROWTH FACTORS AND FLOWERING 



fortunate to get the aid of Dr. Roy Sachs, who generously ran an 

 experiment for us in the CaUfornia Institute of Technology phytotron. 

 Our clone of Coleus was grown there, at a constant temperature of 

 23 °C, under short-day, extended-day, and interrupted-night conditions 

 (8 hr natural light, plus 8 hr artificial light as a supplement). The 

 results confirmed the results above: interrupted nights gave less 

 growth in axillaries-off plants than did extended-day treatments. 



DISCUSSION 



When lateral shoots of Coleus are cut off, the main shoot shows 

 striking compensatory growth and much faster flowering. However, 

 our experiments support the interpretation that the two responses are 

 not causally related to each other. The faster flowering apparently 

 results from releasing the main shoot from auxin inhibition by the 

 laterals, whereas the compensatory growth is from some f actor (s) 

 other than auxin. 



This relation of auxin to flowering in Coleus is particularly interest- 

 ing because we are dealing with a naturally occurring inhibition of 

 flowering in a day-neutral plant. This combination has been studied 

 very little in the past. To summarize the evidence for Coleus: Excis- 

 ing axillaries results in significantly faster flowering (Table I and 

 Fig. 1 ) ; axillaries have been shown in many plants to produce auxin 

 (Went and Thimann, 1937) and the smafl, fast-growing leaves of this 

 clone of Coleus produce large amounts (Jacobs, 1956, Fig. 1); 

 synthetic lAA at 1 % substituted for the axillaries significantly reduces 

 the rate of flowering again, but it has no effect on the compensatory 

 growth of the main shoot (Fig. 3). We conclude, therefore, that in 

 the intact plant the axillary shoots are inhibiting flowering in the main 

 shoot, and that all (or a significant part of) this effect is from the 

 auxin produced by the axillaries. [Before we could say definitely that 

 "all" the effect was from the auxin produced by the axillaries, we 

 would need to determine the auxin production of the axillaries and 

 then to match it exactly with that artificially supplied. Such exact 

 replacement has not been done here — nor, we believe, in any other 

 study of auxin's relations to flowering — although its feasibility has 

 been demonstrated in studies of xylem regeneration in Coleus (Jacobs. 



