Permanence and Location of the Induced State • 87 



what paradoxical that the induced state in Perilla leaves themselves 

 appears indestructible. Attempts by Zeevaart (1958) to remove it 

 were completely unsuccessful, for after various treatments the 

 capacity to bring about flowering was retained. The treatments 

 included exposure of the detached leaves to continuous light of 

 low or high intensity, solutions of a synthetic auxin (naphthalene- 

 acetic acid), high temperatures (up to 5 hours at 42° C), and the 

 respiratory inhibitors dinitrophenol and sodium azide. As long as 

 a leaf survived, so did its induced state. However, Lam and Leopold 

 (1961) have recently obtained results indicating that, under certain 

 circumstances, the induced state in a Perilla leaf may be gradually 



lost. 



One of the most curious properties of the induced state in 

 Xanthium is its quantitative nature. This is not to be confused 

 with the phenomenon previously mentioned (for example, in 

 Biloxi soybean) in which eventual reversion to the vegetative stale 

 is preceded by an "amount" of flowering proportional to the in- 

 ductive treatment. In Xantfiium, too, the intensity of flowering is 

 quantitatively related to the inductive treatment (for example, 

 Salisbury, 1955), but since intact plants do not revert, they merely 

 continue flower development at a very slow rate if the initial 

 induction treatment is minimal. F. L. Naylor (1941) compared the 

 development of plants under repeated short days with that of others 

 given only a single short day and then placed in long-day con-, 

 ditions. In the former, inflorescences with all flower parts complete 

 were evident after 13 days, and the seeds were almost mature within 

 a month. The second group did not show complete flower develop- 

 ment until over two months from the single short day, but the slow 

 progress toward fruiting gave no sign of stopping before the experi- 

 ment was discontinued, shortly thereafter. This kind of observation 

 seems much more difficult to explain than a mere reversion to 

 vegetative growth. The latter could be due to exhaustion of florigen 

 or, as in Perilla, of the capacity to produce it, but maintenance of 

 a long-lived but low "steady state" of flowering cannot be visualized 

 on this basis. In a sense it is analogous to the fractional induction 

 described in Chapter Three, except that in fractional induction 

 there is no morphological or anatomical change after the first, 

 subminimal, treatment. 



There is little to be added here to the description of the state 



