98 THE PEANUT— THE UNPREDICTABLE LEGUME 



LIGHT AND TEMPERATURE RELATIONS 



Peanuts do not appear to be especially sensitive to length of day. 

 The plant seems to grow very well from the tropics to the middle tem- 

 perate zone. The day length in most of that area could be classified as 

 intermediate, which suggests that such is satisfactory for peanut growth. 

 In the United States peanuts are usually planted in April or May and 

 maximum fruit development probably occurs during July and August 

 when the days have begun to shorten. There is little seasonal variation in 

 day length in southern India, and peanuts are sometimes planted in the 

 fall in which case maximum fruit development occurs in the spring when 

 days are lengthening. 



Moore (59) found that Spanish peanuts bloomed abundantly when 

 illuminated continuously for several weeks. Cheliadinora (21, 22) found 

 that longer days increased the green weight and flower production, al- 

 though the latter was not consistent. However, the ratio of fertilized to 

 unfertilized flowers was higher with the short-day plants. Shaded plants, 

 especially those on the shorter photoperiods, had fewer undeveloped pods 

 and gynophores, which was attributed to earlier flowering when a more 

 favorable lime and nutrient supply was available to aid development of 

 fruit which had set. These results indicate the length of day has an effect 

 on the peanut ; however, critical studies of the photoperiodic response are 

 lacking. 



Although the intensity of light would seem to be important, few data 

 have been published in reference to its connection with peanuts. Moore 

 (59) found that when shaded plants were grown with 3- or 4-hour 

 periods of daylight, blooming was practically prevented because of in- 

 duced carbohydrate starvation, while Cheliadinora (21) produced good 

 yields under partial shade. Those results indicate that slight shading is 

 not particularly harmful as is a pronounced shortage of light. 



Peanuts grown in an air-conditioned greenhouse at California Insti- 

 tute of Technology^ required a high day temperature for normal develop- 

 ment. Cool temperatures resulted in chlorosis and poor development. 

 Similar results have been observed at the Florida Station. These obser- 

 vations seem to be in agreement with the results of Cheliadinora (22) 

 that the photoperiodic treatment is effective only when the temperature is 

 favorable during the flowering period. An increase in temperature also in- 

 cteaied the yield of fruit (22), which agrees with the general assump- 

 tion that the peanut is a warm-weather crop. 



^ Personal correspondence, W. P. Jacobs. Princeton University. 



