MICHIGAN ACADEMY OF SCIENCE. 
53 
thus evident that much of the work that has been done will have to be 
repeated under more exact experimental control, the realization of the 
complexity of the problems will do much to remove the present unsatis- 
factory condition. 
But what, after all, is the most unsatisfactory thing from the stand- 
point of the physiologist is the small amount of work that has been done 
on the processes of the plant itself. Little is known about the form in 
which substances enter the plant, and still less about the relation of con- 
ditions in the soil to the internal conditions of the plant and of these 
internal conditions to growth. While these problems are complex, they 
are by no means hopeless and should be of tremendous importance from 
both a scientific and practical standpoint. It may not therefore, be out 
of place here to discuss some of the possibilities. 
Since chemical reactions take place more rapidly in a dilute than in a 
concentrated solution, we would expect growth to be more rapid when 
the solution in the cell is dilute than when it is concentrated, provided, 
of course, that the necessary elements are present in sufficient amount. 
If a submerged plant such as Elodea, is placed in distilled water or in 
a very dilute solution of nutrient salts where the tendency would be 
for the salts to diffuse from the plants to the water and thus weaken 
the solution in the cells, the plant will grow several times more rapidly 
during the first three days than if it were in ordinary pond water. 
Rapid growth does not, however, necessarily mean good growth, and in 
this case, the plant usually dies about the fifth day. Plants growing 
under arid conditions usually have an extremely slow 'rate of growth 
and the concentration of their juices is higher than that of plants grow- 
ing in moist localities. Likewise when plants that have been growing 
under moist conditions are subjected to drought, their juices become 
concentrated and growth is less rapid or may cease altogether. From 
the above observations, it would seem probable that the degree of con- 
centration of the juices of a plant may markedly affect the rate of growth. 
The water content of many plants may be reduced 50 per cent, without 
causing signs of wilting, by decreasing the amount of water in the soil. 
In this case, there must be a great increase in the concentration of the 
solution in the plant cells and an increase in the osmotic pressure. This 
is followed by a great decrease in the amount of water given off by the 
transpiration of the plant. Plants thus give off and take up less water 
when growing in a dry soil than when growing in a moist one. The fact 
that the amount of water in a plant decreases as the soil becomes drier 
should find a ready application in agriculture in regions where irriga- 
tion is practiced, for if the optimum water content of the leaves were 
once determined, it would be easy to tell when the per cent of water fell 
below this. This would indicate that it was time to irrigate, and remove 
all uncertainty. In all probability growing a plant in a concentrated 
solution would have the same effect in increasing the concentration of 
the plant juices as growing it in a dry soil, for the amount of salts taken 
in a plant is not regulated by the amount of water that passes through 
it but by the relation between the concentration outside and inside the 
plant, since the salts move by diffusion and this may be independent 
of the movement of the water. 
It is well known that certain plants will not grow in soils in which 
the water contains a large amount of dissolved salts. When we ask for 
