318 
researches which may be the starting points 
of new lines of progress. At the same time 
I shall seek to indicate what I conceive to 
be fruitful lines of study and shall direct 
attention to some of the unsolved problems 
which still confront the physiologist. 
PHYSICAL CHEMISTRY. 
The physiologist is dealing with material 
phenomena as manifested by living things. 
Physiology is, therefore, chiefly the applica- 
tion of the knowledge of chemistry and 
physics to the phenomena of life. It fol- 
lows that the physiologist must be familiar 
with the laws deduced by chemists and 
physicists from their study of matter which 
is not under the influence of life. He needs 
to be equipped with the best physical and 
chemical knowledge of the day. Because 
of a want of such training reproach has 
often fallen upon physiology in the past. 
Inattention to these underlying sciences has 
led to divers fantastic explanations of 
phenomena—explanations forbidden by the 
fundamental facts of chemistry and physics. 
Compelled thus to rely on advance in other 
sciences for the possibility of progress in 
their own, physiologists welcome with the 
brightest anticipations the rapid growth and 
development of that field in which chemis- 
try and physics merge—physical chemis- 
try. There is much, it is true, with which 
its students concern themselves that does 
not touch directly the activities of plants. 
But some of its subjects are of the most 
intimate concern to physiologists. 
Solutions.—This is notably the case with 
the comparatively recent coordination of 
long known facts and late discoveries into 
clear and definite laws of solutions. Inno 
condition, outside and inside the plant 
body, does matter play a more important 
physiological réle than in a state of solution 
in water. The prevalence of a cellulose 
wall, jacketing the protoplasm of their 
cells, is probably the most characteristic 
SCIENCE. 
[N.S. Vou. X. No. 245. 
mark of plants. This membrane precludes 
the entrance into the body of any substance 
not in solution, whether originally solid or 
gaseous. Thus the behavior of solutions is 
of fundamental importance for the absorp- 
tion of foods by the colorless plants and of 
the raw materials out of which the green 
plants can make foods. 
The cellulose wall has been adapted by 
plants to subserve a function unknown in 
the animal body, namely, turgor. Only 
a knowledge of solutions enables us in a 
measure to understand the existence and 
regulation of turgor. The solutions en- 
closed by the semipermeable protoplasmic 
membrane of the living cell are rarely or 
never the same as those outside the plant 
or in paths of water conduction. Such a 
condition establishes at once a movement 
of water into the cell and develops a definite 
amount of hydrostatic pressure, equivalent 
to the osmotic pressure of the dissolved 
substances. Thus, by a figure, it is said 
that the osmotic pressure of the internal 
solutions pushes outward the protoplasm, 
backed by resistant but elastic wall, which 
stretches until its elastic resistance balances 
the osmotic pressure. If the cell be one of 
a group the cohesion and turgidity of the 
cells surrounding any one resist its enlarge- 
ment. Thus all the cells of a turgid mass 
of tissue bear firmly against one another, 
and this condition is of great importance 
in maintaining the form of young parts in 
which as yet no mechanical tissues exist. 
Turgor has its influence also in regulat- 
ing the diffusion of water vapor through 
the stomata, in transfusing liquid water 
through water glands, in certain forms of 
secretion, and so on. So important is tur- 
. gor that special salts seem to be provided 
to maintain it at a normal point. Its re- 
lations to growth also are unquestionably 
of prime importance, but we are not able 
at present to interpret these relations sat- 
isfactorily. Although the statement is 
