60 THE FLOWERING PROCESS 



urbanuni) also seem resistant to gibberellins so far as flowering is 



concerned, although in some instances stem elongation is promoted. 



It seems clear, then, that gibberellins will often substitute for a 

 vernalization or a long-day requirement (but seldom for both in the 

 same plant) but not for a short-day requirement. It is possible that 

 some of the exceptions might be due to experimental factors. Perhaps 

 the dose was not high enough or applied for a long enough time. Or 

 perhaps the proper gibberellin was not used. Recently Marian 

 Michniewicz and Anton Lang (63) at Pasadena, California, have tried 

 nine different gibberellins on five species of cold-requiring and 

 long-day plants. They found a marked difference in response to 

 these compounds. GA-7, which is relatively new and difficult to 

 obtain, was highly effective in all species, including one which was 

 known to be resistant to the more common gibberellic acid (GA-3). 

 Furthermore, compounds which were effective on one species were 

 in some instances completely ineffective on another species. GA-8 

 was ineffective in all five species. It is quite obvious, then, that work 

 with a single form of gibberellin should not provide a basis for 

 generalizations. 



A primary question concerns whether the gibberellin effect is 

 physiological or pharmacological. To paraphrase Lang and Reinhard, 

 is gibbereUin a picklock that will open a door for which it wasn't 

 actually designed, or is it the natural key to flowering of cold- 

 requiring and long-day plants ? 



There are at least two lines of evidence which indicate that gibberel- 

 lins do indeed play a role in the flowering process under natural 

 conditions. First, they are now known to occur in higher plants, 

 perhaps all higher plants, as well as in the fungi. Although five of 

 the gibberellins used by Michniewicz and Lang were isolated from 

 the fungus Fusarium moniliforme (GA-2, GA-3, GA-4, GA-7, and 

 GA-9), three were isolated from immature bean seeds (GA-5, GA-6 

 and GA-8), and one was found in either source (GA-1). GibbereUins 

 extracted from a number of higher plants have now been used 

 successfully to induce flowering. Perhaps most impressive of all, 

 extracts from plants which are flowering are more effective than 

 extracts from the same vegetative, cold-requiring or long-day species. 



This brings us logically to the second evidence, which is that the 

 gibberellin status of a plant changes markedly during induction by 

 cold or long days. Lang has shown that both the quantity and the 



