Nuttonson — 133 — Phenological Data 



average length of day and the summation of total day-degrees. ^ Measure- 

 ments between these two phenological stages in terms of days or in terms of 

 day-degrees alone provide mathematical expressions of considerable 

 variability. Thus, the date of first heading of Marquis wheat appears to be 

 associated with a response to more than one environmental factor, 

 namely, to a combination of the average length of day and the summation 

 of day-degrees. It appears, therefore, that the temperature must be taken 

 into account in studies dealing with the relation of Marquis wheat to 

 length of day. As may be observed in the table, the first heading on June 

 13 can be interpreted as having been brought about by a combination of 

 2070 day-degrees and 11.4 hours of average daylight while that of the first 

 heading on August 27 as having been brought about by a combination of 

 1605 day-degrees and 14.5 hours of average daylight. Thus, one could 

 say that the first heading of Marquis wheat is brought about by a combina- 

 tion of either relatively higher summation of day-degrees and shorter days 

 or by relatively lower summation of day-degrees and longer days. In 

 other words, the change from vegetative to reproductive stage may occur 

 in Marquis wheat under a number of certain combinations of temperature 

 and length of day conditions. 



As may be seen from Table 2 and Chart 2, the interval between the dates 

 of emergence and heading as well as the intervals between the dates of 

 emergence and ripening provide the least variable mathematical expression 

 when measured in terms of a multiple of the average length of day and the 

 summation of total day-degrees. 



As already noted in the data of Table 1 it appears from the data of Table 

 2 that the heading as well as the ripening of Marquis wheat is brought 

 about under a number of combinations of temperature summations and 

 length of day conditions. Also, that the response of Marquis wheat to 

 length of day seems to be influenced by the total day-degrees summation 

 between the two phenological stages involved and therefore, the tempera- 

 ture must be taken into account in studies dealing with the relation of 

 certain varieties of wheat to light duration. The day-degrees requirement 

 of Marquis wheat from emergence to ripening seems to increase in a south- 

 ward direction, that is, with the shortening of the length of day duration. 

 It could, therefore, be suggested also that the response of Marquis wheat 

 to temperature conditions seems to be influenced by the length of day. 



As may be seen from Table 3 and Chart 3, the interval between the dates 

 of seeding and first bloom of the flax varieties provides a least variable mathe- 

 matical expression when measured in terms of a multiple of the average 

 length of day and the summation of the total day-degrees. This seems to be 

 also true in the case of the interval between the dates of seeding and ripen- 

 ing. It appears, therefore, with these four varieties of flax that the tempera- 

 ture must be taken into account in studies dealing with the relation of 

 certain varieties of flax to light duration as the response of some flax 



^ The summation of day-degrees, also known as the remainder indices, consists of 

 the summation of all mean daily temperatures above a certain "zero" temperature. In 

 this paper 32°F. for wheat and flax and 40°F. for peas and eggplants have been used 

 as "zero" temperatures. The procedure is to have the zero temperature subtracted 

 from the mean daily temperature between certain phenological events and the remainder 

 multiplied by the total number of days between dates of any two phenological stages 

 under consideration. 



