134 BOTANICAL GAZETTE [avcust 
is a characteristic of the morphology of living organisms. That 
same sort of bridging is no less characteristic of their physiological 
processes. For example, we find all stages of dependence upon 
oxygen, from plants which are killed by its absence to those which 
are killed by its presence. It is not inconceivable that there exists an 
analogous range of differences in the means which various plants take 
to accomplish the cleavage of their metabolic proteids. 
At any rate it has been shown by the researches of various inves 
tigators that enzymes are present in animal and vegetable tissues of 
both the tryptic and ereptic type. There has not yet been found a 
tissue which has been definitely shown to contain no proteolytic 
enzymes whatever, and which must therefore complete its processes 
of proteolysis by the activity of its protoplasm. Our knowledge 
too limited to allow us to say that such tissues do not exist; that point 
must be left for future investigations. 
The investigation, of which this is a report, was carried out with 
the assistance of a grant from the Carnegie Institution of Washington. 
LABORATORY OF PLANT PHYSIOLOGY, 
SHEFFIELD SCIENTIFIC SCHOOL, 
YALE UNIVERSITY. 
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