vili VEGETABLE PHYSIOLOGY 
more complete discussion of the subject which may be 
met with in the advanced textbooks of Sachs, Vines, and 
Pfeffer. 
With this view I have endeavoured to present the 
plant as a living organism, endowed with particular 
properties and powers, realising certain needs, and meet-~ 
ing definite dangers. I have attempted to show it to be 
properly equipped to encounter such adverse conditions, 
and to avail itself of all the advantages presented to it 
by its environment. 
I have also set before myself another purpose, which, 
however, is naturally subordinate to the one just mentioned. 
When we consider the origin of the different organisms 
which we find around us, we are led irresistibly to the 
conclusion that the classification of living beings into 
animals and plants has been too strongly insisted upon in 
the past, and that while much has been made of their 
differences, their points of resemblance have been mini- 
mised. The fact that organisms exist, which it is difficult or 
impossible to refer with certainty to either kingdom, points 
to a fundamental unity of living substance. Protoplasm 
in short is the same material, whether we call it animal or 
vegetable. This being the case, its conditions of life and its 
immediate necessities must be practically the same, what- 
ever its degree of differentiation in either direction. I 
have tried to bring out this identity of living substance 
throughout the book, and to indicate that apparent differ- 
ences of behaviour and structural arrangement are to be 
traced rather to differences of environment and habit of 
life than to those of constitution. The correspondence of 
the processes of respiration in animals and plants has long 
been recognised; many points of similarity in those of 
nutrition have been observed. The idea is, however, still 
