SOME PRELIMINARY OBSERVATIONS OF PHE- 

 NOLOGICAL DATA AS A TOOL IN THE STUDY 

 OF PHOTOPERIODIC AND THERMAL REQUIRE- 

 MENTS OF VARIOUS PLANT MATERIAL 



by 

 M. Y. NUTTONSON 



Formerly Senior Agronomist, Technical Collaboration Branch, Office of Foreign Agricultural 

 Relations, U. S. Department of Agriculture 



The effect of the relative length of day and night upon growth and re- 

 production in plants has been studied since 1920 when Garner and Allard 

 first focused the attention of plant physiologists on the phenomena of 

 photoperiodism. 



Our present day concepts in regard to the fundamentals of plant growth 

 and plant responses to light duration are largely due to investigations con- 

 ducted under controlled or semicontroUed conditions in the laboratory, 

 greenhouse, or field. 



The present objective of the writer is merely to suggest on the basis of 

 preliminary studies of fairly extensive agronomic and horticultural data 

 that there appears to be an "uncontrolled" field method which can be used 

 to ascertain and to establish the nature of photoperiodic responses of vari- 

 ous plants. These responses, it is believed, could be studied through the 

 use of phenology and phenological records of horticultural and agronomic 

 varieties of plants grown under uncontrolled field conditions in a great 

 number of geographical-climatic areas. 



The dictionary defines phenology as a science dealing with the rela- 

 tion between climate and periodic biological phenomena. Dates of sowing 

 or planting of crops, dates of germination or emergence, dates of stooling 

 or tillering, dates of leaf bud opening, dates of shooting, dates of blossom- 

 ing or heading, dates of terminal bud formation, dates of various distinct 

 stages of biological or market maturity of genetically homogeneous clones 

 or pure line horticultural varieties are the kind of phenological data the 

 writer has in mind. 



Phenological records are most often gathered as incidental data in the 

 course of various agronomic and horticultural field studies. The utiliza- 

 tion, if any, of such records has been so far mainly of a very limited and 

 local nature. Studies of varietal adaptation, quantitative and qualitative 

 yield studies, plant breeding studies, disease and pest problem studies, etc. 

 are all sources of phenological material. Experimental and commercial 

 plantings of the same varieties in various localities, plantings of the same 

 varieties during various years in the same locality, and plantings of the 

 same varieties during various seasons of the same year in the same locality 

 as well as time of planting studies of the same varieties during any given 



