NUTRITION AND METABOLISM AS RELATED 

 TO PHOTOPERIODISM 



by 



A. E. MURNEEK 



University of Misscmri, Columbia, Missouri 



In consideration of the relationships between nutrition and metabolism 

 and sexual reproduction as effected by the photoperiod, one should dis- 

 tinguish clearly the various stages of reproduction, from inception of floral 

 primordia to flowering and fruit production. Unfortunately this has not 

 been done in the vast majority of instances in nutritional studies and inter- 

 pretation of chemical analyses of plants. Moreover, in sampling material 

 for chemical assays one should keep in mind the fact, so aptly stated by 

 LoEHWiNG (13) that at any given time similar organs of a plant may be in 

 various stages of development. Parts of the tissues on the same plant or 

 portions thereof may range from juvenile to senescent states and through 

 all stages of reproductive development. This is particularly true of plants 

 with an indeterminate type of growth. Disregarding of these facts, as 

 in chemical analysis of whole plants or large portions of them, has re- 

 sulted in accumulation of recorded data that are difficult or impossible to 

 interpret and therefore of little value. 



Most of the earlier nutritional and chemical studies on photoperiodism 

 were influenced by or interpreted by means of the carbohydrate-nitrogen 

 relationship concept, which was advanced by Klebs and re-emphasized by 

 Kraus and Kraybill shortly before the announcement of the discovery of 

 photoperiodism. Plants exposed to certain lengths of day have been grown 

 under various regimes of soil nutrient supply with particular emphasis on 

 nitrogen and the observed results, as regards time and amount of flower 

 development roughly recorded. In many instances concomitant chemical 

 analyses for carbohydrates and nitrogen compounds have been made. The 

 results of the earlier work have been reviewed critically by the writer and 

 others and therefore need not be recapitulated here (Murneek, 21, 22; 

 LoEHWiNG, 12, 13). In general the information thus secured is very con- 

 flicting and concerns largely observations of plants in comparatively late 

 stages of vegetative and reproductive development. Therefore, it is very 

 little, if at all, applicable to the problem of relation of nutrition and meta- 

 bolism to induction of the sexual state by the photoperiod. The evidence, 

 however, is indicative to some extent of the nutritive states of plants in 

 various stages of flowering and fruiting (if definitely specified), at which 

 condition in most instances the plants were sampled. 



Some relatively recent studies on nitrogen nutrition in relation to photo- 

 periodism should be referred to here. In her investigation with several long- 

 and short-day plants, including Soja and Xanthium, Withrow (31) comes 

 to the conclusion that the external nitrogen supply is not as determining a 



