plants manufacture certain sugars from the carbon dioxide of the atmosphere 
and the water within their stems, through action of light upon their chlorophyll 
cells and that, by processes not yet completely understood, these sugars are con- 
verted into starch or mucilage and other carbohydrates, and into proteins, organic 
acids, fats, and so on. It is obvious, therefore, that light of some sort is essential 
to the growth of every plant. For some years this relationship between light 
and plant life has been the subject of scientific investigation. 
Experiments have been made in specially constructed chambers in which heat 
and moisture were controlled, and which were so screened that certain rays could 
be blocked while others were permitted to enter the chamber. These experiments 
were not only conducted with sunlight, but with various forms of artificial light 
such as mercury arc and tungsten lamps. The compilation of the results from the 
data obtained has not been completed, but it would appear that the red rays are 
the most promotive of growth, the blue rays next best, while the green and yellow 
rays are useful—but the infra-red and the ultra-violet rays contribute nothing 
to the growth of the plant. 
Investigations into the relationship between light and the flowering of plants 
have been carried on for some years, particularly by Dr. Garner and Dr. Allard, 
of the United States Department of Agriculture, and, as a result of these inquiries, 
it has been demonstrated that the production of flowers in many types of plants 
may be increased or reduced by the regulation of the daylight available to them. 
A number of plants are not noticeably affected, but the majority fall into one of 
two groups: (1) “long-day” plants, and (2) “short-day” plants. 
In the case of the long-day plants, it was shown that, in order that they 
produce flowers at all, they must have a certain minimum daily exposure to sun- 
light. If this critical light period was increased, the flowering stage was reached 
more rapidly, and the quantity of flowers produced was increased—and this im- 
provement was continued by increasing the period of light up to a maximum, 
after which no further improvement was noted. In fact, a tendency to deterior- 
ate was noted in some instances, and in others an increase of foliage growth at 
the expense of the flowers. 
When the light periods were reduced below the critical period there was a 
cessation of flowering and a retardation of growth. 
In the case of short-day plants, the results were practically reversed. An 
increase of light over the critical period tends to reduce or prevent flowering, 
while a reduction of the light period increases the quantity of flowers and hastens 
the flowering period. Experiments with artificial lights had similar results, 
Now, as far as I can ascertain, no experiments have been carried out under 
research conditions with Orchids as their subject. Just before the war broke out 
I made certain arrangements for the supply from America of certain lamps which 
emit various rays—red, yellow, blue, etc.—with the intention of conducting ex- 
periments with Orchids along the lines mentioned, but unfortunately, as a result 
of the hostilities, I was not able to obtain them. However, when happier times 
return, I hope to be able to go ahead with my plan. I am quite confident that 
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