Coleus blumei Bcnth 403 



1956). But there is some reason to think that fairly exact matching is 

 done by the plant, through the controlling action of the transport 

 capacity of the stem for auxin (Jacobs, 1950a,b, 1954).] 



There are already in the literature many reports of slower flowering 

 following auxin application (review in Bonner and Liverman, 1952). 

 This report differs from most in that (1) it concerns a day-neutral 

 plant (as contrasted to SDP and LDP, which have been most 

 thoroughly studied); (2) in being concerned with a natural flower- 

 inhibiting effect of plant organs; (3) in substituting auxin for excised 

 organs (instead of artificially increasing the natural auxin levels by 

 spraying or immersing the intact organs); and (4) by providing more 

 detailed evidence that the vegetative growth is unchanged by the 

 auxin while flowering is being inhibited (cf. Figs. 3 and 5). 



Leopold (1949) has observed in this clone of Coleus that more 

 auxin diffuses from leaves kept under LD than under SD conditions. 

 This result suggests that the somewhat slower flowering which we 

 observed under LD conditions is also caused by auxin and is real 

 (although not statistically significant in our experiments). 



When interrupted night was used instead of extended day, an inter- 

 esting effect appeared. Although the flowering rate was unchanged, 

 much less compensatory growth occurred than under extended day, or 

 even than under SD. There was no discernible effect on normal growth, 

 i.e., when the axillary shoots were left intact, interrupted nights gave 

 no differential effect in growth of the main shoot. 



An inhibiting effect of interrupted nights on the "normal" growth 

 of tomato plants has recently been described by Highkin and Hanson 

 (1954). For growth at constant temperature, they found small but 

 significant decreases in height and weight in plants treated with a 2-hr 

 interruption of the night as contrasted to a 2-hr extension of the day. 

 These differences could be increased if the plants were grown entirely 

 under low-intensity artificial light (as contrasted to 8 hr of sunlight). 

 By contrast, light during the night had no significant effect on sun- 

 flowers, and only a small effect on peas. 



Can the inhibiting effects of interrupted night on growth of Coleus 

 and tomato be basically similar, even though the inhibition has been 

 found for normal growth in tomatoes but only for compensatory 

 growth in Coleus? We think they are, but that tomato is much more 



