232 



CHEMICAL AGENTS AND GROWTH 



Fig. 5. Lowell peach seedlings produced by unchilled embryos dis- 

 sected out of the seeds. Left, plants having received each about 5 jig of 

 gibberellic acid in lanolin. Right, untreated controls. Photographs taken 

 1 month after the treatment (Nitsch, 1957a). 



similarly treated with gibberellic acid, remained under long, 18-hr 

 days. The plants under 18-hr days grew regularly, the ones treated 

 with gibberellic acid growing significantly faster than the untreated 

 ones. Under short days, the untreated group stopped growing com- 

 pletely after 2 weeks, the terminal growing points abscising, which 

 caused a slight diminution in the overall length; the gibberellic acid- 



+ GA 



10-HOUR DAYS 



Fig. 6. Average stem growth of Rhus typhina seedlings moved at time 

 from long days to long, 18-hr days or to short, 10-hr days. The dotted 

 lines represent the average growth of plants treated with about 10 /xg 

 of gibberellic acid at time (Nitsch, 1957b). 



