No. 3. — The Role of Water in Growth> 
By C. B. Davenport. 
In this paper it is proposed, first, to consider the definition of 
growth in organisms; next, to analyze the processes of growth; 
then, to show what an important part water plays in' growth and the 
significance of this fact for the developmental process in general; 
and, finally, to discuss the bearing of the new facts brought forward 
upon previously formulated laws of growth. 
Organic growth I shall define as increase in volume. It has been 
variously defined by others. Thus Huxley has called growth 
“increase in size,” which is essentially the same definition. Sachs 
defines growth as an increase in volume intimately bound up with 
change of form (“ eine mit Gestaltveranderung innig verkniipfte 
Volumenzunahme ”), and he illustrates the definition by the example 
of the growth of a sprout from its beginning to its completed form. 
In this case two phenomena are distinguishable: first, increase in 
volume, and, secondly, the filling out of the details of form. As 
Sachs says, these phenomena taken together are generally denom¬ 
inated “ development,” and it seems to me decidedly advantageous 
to retain this term with its usual signification and to distinguish the 
two component processes by the terms growth and differentiation. 
Pfeffer’s definition differs still more widely from mine. He 
defines growth as change in form in the protoplasmic body (“ die 
gestaltliche Aenderung im Protoplasmakorper ”), and he goes on to 
say that increments of volume and mass are not proper criteria of 
growth. Pfeffer illustrates this statement by the following example : 
A plant stem or a cell membrane can be permanently elongated by 
extension beyond the limits of elasticity, without the volume neces¬ 
sarily increasing, and he apparently means to include such an 
artificial deformation in his definition of growth. “ And,” he con¬ 
tinues, “ under certain circumstances a diminution of volume of a 
plant segment can indeed occur as a result of growth, when, for 
example, the elasticity of the wall is increased by growth and water 
is pressed from the cell until equilibrium is restored ”; I doubt, 
1 Contributions from the Zoological Laboratory of the Museum of Comparative Zool¬ 
ogy at Harvard College, E. L. Mark, Director, No. 80 . 
