Vernalization and Photoperiodism — 142 — A Symposium 



fluenced by the temperature conditions and hence the temperature must be 

 taken into account in studies deahng with the relation of peas to Hght 

 duration. 



The data of Table 6 and Chart 6 also suggest the multiple of day-degrees 

 summation and average length of daylight as the least variable expression 

 for measuring the interval between two phenological stages in Alaska peas. 

 As may be seen from the data in this table the interval between planting 

 and harvest seems to have taken 912 day-degrees at an average length of 

 day of 19.1 hours in Alaska and 1359 day-degrees at an average length of 

 day of 13.6 hours in Maryland. Thus, again the response of Alaska peas to 

 length of day appears to be associated with the temperature conditions to 

 which they are subject. Hence, the temperature must be taken into account 

 in studies dealing with the relation of certain varieties of peas to light dura- 

 tion. With these data too the day-degree requirement of Alaska peas from 

 planting to harvest seems to increase in southward direction, that is, with 

 the shortening of the length of day duration. 



As may be observed in Table 7 and Chart 7 the interval between the 

 dates of seeding to market maturity of the Black Beauty eggplant provides 

 the least variable mathematical expression when measured in terms of a 

 multiple of the average length of day and the summation of the total day- 

 degrees. No comparison is attempted between dates of seeding and "set 

 in field" as the latter does not represent a clear-cut end point of any phe- 

 nological stage- 

 It appears that with the Black Beauty eggplant the amount of day- 

 degrees required to bring about the earliest market maturity stage in- 

 creases southward, that is, with the decrease in the duration of the average 

 length of day. Hence, the temperature must be taken into account in 

 studies dealing with the response of certain varieties of eggplants to light 

 duration as it is the joint effect of the two factors that seems to be in- 

 volved here rather than light duration or temperature alone. 



Summary and Discussion 



I. Through the assembling of phenological data already available for a number 

 of varieties of various crop species some preliminary evidence is presented to show 

 the possibility of using such data to disclose and to ascertain the photoperiodic and 

 thermal requirements of an horticultural variety grown under uncontrolled field 

 conditions. 



II. Phenological data utilized in this paper pertains to the following plant 

 varieties and geographical areas in North America: (i) Phenological data of 

 Marquis wheat (a) from a time of planting study at Moro, Oregon; and (b) from 

 experimental plantings at Fairbanks, Alaska ; Beaver Lodge, Alberta ; Saskatoon and 

 Indian Head, Saskatchewan; Portage la Prairie and Winnipeg, Manitoba; Havre, 

 Montana; Dickison, North Dakota; Alliance and Lincoln, Nebraska; and Tlalne- 

 pantla, Mexico. (2) Phenological data of four varieties (Linota, Redwing, Bison, 

 and Rio) of flax from experimental plantings at Fairbanks, Alaska; Edmonton, Al- 

 berta; Saskatoon, Saskatchewan; Morden, Manitoba; Crookston and St. Paul, Min- 

 nesota; Bozeman, Montana; Corvallis, Oregon; Madison, Wisconsin; Logan, Utah; 

 Fort Collins, Colorado; Manhattan, Kansas; and El Centro, California, (i) Phe- 

 nological data of Alaska peas (a) from a time of planting study at College Park, 

 Maryland; and (6) from experimental and commercial plantings at Matanuska, 

 Alaska; Rochester, New York; State College, Pennsylvania; and College Park, 

 Maryland. (4) Phenological data of Black Beauty eggplant from experimental 

 plantings at Storrs, Connecticut; Beltsville, Maryland; Davis, California; Gaines- 

 ville, Florida; and Winter Haven, Texas. 



