130 
The utilization of water falls and the em- 
ployment of solar engines come under the 
first head. Here in the West we are utiliz- 
ing, in electrical form, a considerable 
amount of energy from water falls and 
rapids, and have only just begun on the 
development of the possible power sites of 
the region. While many other localities 
can develop considerable amounts of 
energy in this way, not all portions of the 
earth are so well favored. Solar engines are 
reported to be in successful operation in a 
few places where the total annual amount of 
sunshine is unusual. Hven with the full 
use of hydroelectric power and of solar en- 
gines, the situation, while not appearing 
serious for the immediate future, is such as 
to cause us to look with interest at the 
possibility of alcohol and other plant prod- 
ucts as a source of energy. 
In addition to the uses above mentioned 
for this energy, it may also function in 
other processes going on within the plant 
and necessary for its life and growth, and 
thus for its continuing to function in ma- 
king possible the existence of human life 
on the earth. The intake of water by the 
plant from the soil solution seems to be 
mainly through the process of osmosis, al- 
though there seems to be much reason now 
for believing that we have been placing en- 
tirely too low an estimate on the part 
played by imbibition. In either case, the 
energy for the intake of the enormous quan- 
tities of water evaporated from the plant 
as well as the considerable amount used in 
the synthesis of food substance resides in 
the substances elaborated by the plant from 
the raw materials taken in from air and 
from soil solution. 
Osmosis and imbibition are processes 
whose energy is largely traceable ultimately 
to the photosynthetic activity of the plant 
itself or of other plants either recently or 
in the remote past. Among the important 
SCIENCE 
[N. 8. Von. XLVIII. No. 1232 
results of this intake of water is the main- 
tenance of form in the softer parts of 
plants, due to the fact that their cells are 
so full of water as to be turgid. Every- 
one is familiar with the loss of form by the 
leaves and young stems in wilting, 7. eé., 
a loss of the turgidity of its cells. 
Considerable amounts of work are done 
by plants in their mechanical effect on ob- 
stacles that come in the way of their 
growth. Striking evidence of this was seen 
on the campus in the spring of 1910 where 
the large ferns buried under the asphalt 
put down on the campus roadway during 
the preparation for the exposition of 1909, 
burst through these roadways at numerous 
points and continued thealthy growth until 
trodden down by the increasing number of 
students and faculty of the university. By 
the further expenditure of energy the 
plant increases the extent of its own tissue 
by cell division and by the thickness of the 
walls of these cells, resulting in rigid tissue 
which are the main factor in the mechanical 
strength of older woody portions of plants. 
This energy comes to the aid of man in sup- 
plying wood and coal for fuel and for the 
various uses which wood finds in the struc- 
tures incident to modern civilization. 
There are other minor uses for the radi- 
ant energy received by the plant from the 
sun. Under certain conditions a limited 
amount of it may go to keep up the tem- 
perature of the leaf to that of the surround- 
ing air. A certain amount of the sun’s 
energy finds its use in the locomotion of the 
adult form of a few lower plants and of 
minute reproductive bodies in many higher 
plants. A small amount through oxida- 
tion results in the production of luminosity 
in a limited number of plants. 
The plant uses this energy inefficiently. 
The potential energy stored up in the plant, 
as measured by determining the heat of 
combustion, is only 1 per cent. to 5 per 
