409] E. 8. Johnston 911 
SEASONAL VARIATIONS IN THE GROWTH-RATES OF 
BUCKWHEAT PLANTS UNDER GREENHOUSE 
CONDITIONS 
By Hari 8. JoHNston 
Seasonal variations in greenhouse plants are of considerable 
importance to plant growers as well as to experimenters in 
plant physiology, but it is especially with reference to physi- 
ological experimentation that this study was undertaken. 
When it is necessary to repeat an experiment on plant growth 
it often occurs that the results of the second experiment are 
in more or less pronounced disagreement with those of the 
first. Since the controlled external conditions must be re- 
garded as the same for both experiments, such disagreement 
appears to be related either to initial differences in the plants 
used (internal conditions) or to uncontrolled external con- 
ditions as these vary with the season. The first of these pos- 
sibilities is probably not as important as the second in most 
cases, for care is usually taken to select plants for the second 
experiment that are apparently similar to those used for the 
first. While this problem of similarity of internal conditions 
of different lots of plants is a very difficult one and is hardly 
susceptible of quantitative study at the present time, it is 
quite possible to carry out studies on the relation of growth 
to the usually uncontrolled (or only partially controlled) 
external conditions of a greenhouse, as these conditions 
change throughout the year. A portion of the results ob- 
tained from such study are here presented. 
A set of similar water cultures was started every two weeks 
and each was continued for a period of four weeks, so that 
the periods of successive sets overlapped. A single set con- 
sisted of ten plants, each suitably supported in a glass jar con- 
taining about 425 cc. of nutrient solution. These jars were 
covered, to exclude most of the light from the plant roots. 
The solution was renewed at the middle of each four-week 
