Robert B. With ro w 397 



Conversely, certain long-day plants in a long photoperiod favorable 

 for flowering and deficient in nitrogen tend to develop macroscopic 

 flower buds earlier than high nitrogen plants. This has been found to 

 be true with barley (j), hard wheat (7), Iberis (7), spinach (28, 5$), 

 and lettuce (7). In a long photoperiod, the rate of growth is not de- 

 creased to the same extent by decreasing the nitrogen supply as it is 

 in the case of a short photoperiod (5#). In this same relation, Scully 

 et al. (45) found that in onion, which is a long-day type of plant and 

 forms bulbs only in a long day, a low nitrogen level tends to accelerate 

 the rate of development of bulbing. These observations do not sub- 

 stantiate the oft-repeated horticultural concept that a low nitrogen 

 level hastens maturity and the flowering of plants. This correlation 

 appears to exist only for certain of the long-day and possibly the day- 

 neutral types of plants. 



B 



oron 



The rate of appearance and severity of several of the micronutrient 

 deficiency symptoms have been found to have a definite relation to 

 photoperiod. Warington (55) observed that plants growing on a boron- 

 deficient medium during the spring and fall months required a longer 

 time for the development of the typical deficiency symptoms than 

 similar plants grown during the summer. She investigated the possible 

 relationships between temperature and day length to these observations 

 and concluded that it was a photoperiod-controlled reaction. With 

 broadbean, scarlet runner bean, Mandarin soybean, and barley, a nine- 

 hour day very definitely retarded the appearance and progress of the 

 boron deficiency symptoms as contrasted with a normal day length 

 of over 15 hours. Biloxi soybean and garden pea exhibited no delay in 

 appearance of symptoms in relation to photoperiod. The deficiency 

 symptoms characteristic of lack of boron were similar regardless of 

 time of appearance. 



MacVicar and Struckmeyer (34) further demonstrated that Xan- 

 thium, tomato, sunflower, and buckwheat exhibited the usual boron 

 deficiency symptoms in a boron-deficient medium during a 16-hour 

 photoperiod. In a short photoperiod of nine hours, the deficiency symp- 

 toms did not appear in these plants. These experiments were conducted 



