DIFFERENCE IN INTERNODE LENGTHS BETWEEN, AND 
EFFECT OF VARIATIONS IN LIGHT DURATION UPON, 
SEEDLINGS OF ANNUAL AND BIENNIAL WHITE SWEET 
CLOVER 1 
By A. J. Pieters 
Agronomist, Clover Investigations, Bureau of Plant Industry, United States Depart¬ 
ment of Agriculture 
HISTORICAL DATA 
The effect of environment on' the growth of plants has probably 
been studied more extensively by Klebs than by any other worker. 
He studied not only the effect of various salts, of temperature and 
moisture, but in his later papers touched on the effect of illumina¬ 
tion for different periods on the blossoming of Sempervivum. 2 In 
this he showed that the blossoming of Sempervivum dlbidum and 
S . funTcii could be affected by varying the hours of illumination to 
which rosettes were subjected while flower buds were forming. 
Later Garner and Allard 3 studied the effect of varying periods of 
illumination on a number of plants and established the fact that in 
many cases at least the blossoming of a species depends on the hours 
of illumination. 4 
In a second paper, 5 Garner and Allard touch on the apogeotropic 
response to photoperiodicity. .They found that increasing the length 
of day increased the total stem length of Amaranthus hispidm and 
other plants, but that the reverse was true of sorghum and certain 
small grains. They do not state whether this lengthening of the 
axis was in the form of increase in the number of intemodes or increase 
in the length of each internode. In Melilotus alba , the increased 
length was due wholly to an increase in the length of each internode. 
The experiments just referred to showed, as did those of Oakley and 
Westover, that the length of the period of illumination may be 
expected to influence not only the blossoming but also the vegetative 
growth of the plant. Under a short day the internodes were short¬ 
ened, while under a long day they were very greatly elongated. The 
degree to which the seedlings were affected varied somewhat with the 
variety. Doubtless other plants will be found to react in a similar 
manner. 
EXPERIMENTAL DATA 
In August, 1921, seeds of annual and of biennial white sweet clover 
were planted in parallel rows at the Arlington Experiment Farm, 
Rosslyn, Va. On October 4, 1921, it was noted that the annual 
plants were taller than those of the biennial, though the number of 
1 Received for publication October 16, 1924; issued October, 1925. 
2 Klebs, G. ueber die blAtenbildung von sempervivum. Flora (N. F. 11/12) 111/112:128-151, illus. 
1918. 
3 Garner, W. W., and Allard, H. A. effect of the relative length of day and night and other 
FACTORS OF THE ENVIRONMENT ON GROWTH AND REPRODUCTION IN PLANTS. Jour. Agr. Research 18: 553- 
606, illus. 1920. 
* As Garner and Allard have already adequately reviewed the literature in their two papers, no attempt 
to do so is made in this paper. 
s Garner, W. W., and Allard, H. A. further studies in photoperiodism, the response of the 
plant to relative length of day and night. Jour. Agr. Research 23: 871-920, illus. 1923. 
Journal of Agricultural Research, 
Washington, D. C. 
( 585 ) 
Vol. XXXI, No. 6 
Sept. 15,1925 
Key No G-501 
