AveustT 9, 1918] 
cent. of the total energy received from the 
sun. Thus 95 per cent. to 99 per cent. of 
the energy received is dissipated by the 
plant. 
The energy point of view has helped 
greatly in clarifying our methods of think- 
ing on biological problems. As a result we 
are now experimenting along lines that 
give great hope for future success. 
Luminosity in plants was for a long time 
an intangible will-o-the-wisp—a founda- 
tion for belief in ghosts. It was not until 
it was studied as an oxidation that the 
facts were established and the mystery 
cleaned up. 
Our study of the intake of water by 
plants from the soil solution has in the 
past consisted too much in the substitu- 
tion of the word ‘‘osmosis,’’ for any clear 
notion of the nature of the processes that 
really take place. A good deal of thought 
unfortunately not so far resulting in much 
experimentation is now being directed 
toward the nature of the energy involved 
in the two processes for which we use the 
names ‘‘osmosis’’ and ‘‘imbibition.’’ 
Considerable more thought and experi- 
mentation have gone into attempts to 
understand the kinds and magnitude of the 
energy involved in the raising of water to 
the tops of plants. The chief progress in 
this field during recent years has been the 
result of thinking in terms of energy. 
Among the many important economic 
contributions made by botanists during the 
last few years, a piece of work by Briggs 
and Shantz‘ on crop plants for arid re- 
gions well illustrates the usefulness of 
thought along energy lines. Plants that 
flourish without irrigation in these arid re- 
gions must, of course, be able to get along 
with very little water. They found that 
the efficiency with which these plants use 
radiant energy is inversely proportional to 
4J. Agr. Res., 3: 1-63, 1914. 
SCIENCE 
131 
their water requirement. Hence, instead 
of introducing from more humid regions the 
plants of high water requirement and try- 
ing to supply to their roots all of the water 
that they can use, a more profitable line of 
endeavor seems to be that of the reduction 
of the water requirement of varieties of 
crop plants that are to be grown in these 
regions. There are two lines of endeavor 
that seem hopeful in this—the selection 
of varieties having low water requirements 
and the lowering of the evaporation rate 
by artificial means, thus lowering the water 
requirement of the plant. 
The field of photosynthesis is an ex- 
tremely important one for the use of the 
energy point of view. All of the probable 
steps in the synthesis of carbohydrate from 
inorganic nature have now been repeated 
in the laboratory. In the main, however, 
this has been accomplished by employing 
forms of energy probably not available in 
the plant. The search for the energy that 
may be available for this synthesis should 
engage much of the attention that is now 
going merely to a consideration of the ma- 
terials involved. 
Some confusion on the energy involved 
in the process has resulted in the past from 
the fact that a few of the earlier workers 
had differences in intensity when they 
thought they had only differences in wave 
length. However, clearer thinking and 
better apparatus are already pointing to 
definite progress in this field. The photo- 
electrie cell has already been employed in 
plant physiology as a means of measuring 
the light intensity under which the plant 
is carrying on its life processes and impor- 
tant data will undoubtedly be obtained 
through its use by future investigators. 
The energy point of view has already 
helped greatly in our understanding of car- 
bohydrate synthesis in plants and prom- 
ises still more in the future for progress in 
