Mar. 17, 1923 
Further Studies in Photoperiodism 
877 
seed, whereas the io-hour plants produced no seed. One of the control 
plants was transferred October 2 to the greenhouse electrically illumi¬ 
nated at night and under these conditions continued in the vegetative 
state without flowering throughout the winter. 
Roots of goldenrod {Solidago juncea Ait.) were transferred to the 
greenhouse November 15, one lot receiving only natural daylight while 
the other lot received the electric illumination from sunset till midnight. 
Under the lengthened illumination period flowering began March 15. 
Beginning March 10, the plants in the control house were placed in a 
dark cabinet for a portion of each day so that they received only 7X 
hours of light daily. In one instance a short, weak flowering stem 
developed as a result of the stimulus from the natural increase in day 
length before the transfer to the dark cabinet was begun. The remain¬ 
ing plants formed no stems but continued to form rosettes of leaves as 
the older leaves perished (PI. 5, B). This type of activity, with complete 
suppression of stem development, persisted throughout the duration 
of the experiment, a period of more than 18 months. 
Cuttings of hedge bindweed {Convolvulus septum L.) exposed to 10 
hours of light daily, beginning May 13, developed no flower buds, whereas 
the controls, exposed to the full day length, were in blossom June 30. 
Other lots of cuttings were exposed to different daylight periods, begin¬ 
ning June 7. The controls, as well as the plants receiving 13 hours of 
light daily, formed numerous flower buds and began blossoming June 28 
to 30. Under a 12-hour day only three flower buds were formed on two 
plants, and under an 1 i-hour day no flower buds at all appeared. 
Seed of winter and spring varieties of wheat {Triiicum vulgare U), rve, 
(Secale cereale U.), oats (Avena saliva I,.), and barley ( Hordeum vulgare U.) 
furnished by the Oiflce of Cereal Investigations, Bureau of Plant Industry, 
were planted in the electrically lighted and the control greenhouse units on 
November 29. The greenhouse was kept relatively warm, the tempera¬ 
ture usually running 55 0 to 6o° F. at night and 70° to 8o° during the day. 
The behavior of the plants under the two conditions of illumination is 
summarized in part in Table II. 
These results with the small grains are too limited in scope and extent 
to justify final conclusions, but they seem to show clearly that detailed 
study of these crops in their reactions to day length would give very inter¬ 
esting and valuable results. It appears that a fundamental distinction 
between the winter and spring types as such rests on the rapidity with 
which the latter respond to the increasing day length of spring. 4 The 
forcing action of the electric light on the spring types resulted in sparse 
fruiting, possibly because of the low intensity of the light. 
4 Since this paper was written Wanser has published in Science (Wanser, H. M. photoperiodism op 
wheat; a determining factor in acclimatization. In Science, n. s., v. 56, p. 313-315* i92a) an inter- 
esting account of a preliminary experiment dealing with photoperiodism in wheat, in which distinctive 
photoperiods are found for the jointing and the heading stages in winter wheat. The fundamental differ¬ 
ences between winter and spring varieties of the small grains in their response to length of day brought 
out in the above data are confirmed by Wanser’s results with wheat. 
27975—23 - i 
