[Vor. 4 
218 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
present, inhibitory factors are also present which hold it in 
check, determine its reactions, and do not allow it to be 
formed to such an extent as to exert pathological influences. 
It is of course true that we have no basis for assuming that 
this supposed enzyme is the initial cause of the disease, and 
may be considered by some as a result of the disorder, but 
we are nevertheless forced to the conclusion that when this 
supposed enzyme is injected in an active form into healthy 
plants, it is capable of stimulating its further production, 
and therefore we have reason to believe that it is the causal 
agent in all cases. The physiological conditions which deter- 
mine its production form the nucleus of another problem. 
A point which may seem to be greatly in favor of the 
‘‘virus’’ theory is that the extract may be diluted 1:1000 or 
even 1:10,000 and still retain the capacity of inducing the 
disease in healthy plants. It is a well-known fact, however, 
that nearly all chemical reactions reach their termination 
better and more completely when the chemicals are brought 
together in relatively dilute concentrations. This is particu- 
larly applicable to substances of a colloidal nature. Chemical 
reactions resulting from the activity of such colloidal com- 
pounds as enzymes, are largely dependent upon the adsorp- 
tive power of these enzymes. If, then, they are present in 
relatively dilute concentrations, the colloidal particles will be 
more dispersed, the opportunity for adsorptive phenomena 
greater, and chemical action free to proceed in its normal 
course. If the enzyme producing mosaic diseases is extremely 
active, one may easily understand how great dilution would 
yet enable it to induce metabolic disturbances. When reac- 
tions of this kind are carried on in vitro, the activity, on ac- 
count of a limited amount of material, will ultimately cease. 
In a living organism, however, the situation is entirely dif- 
ferent. More compounds are constantly being formed as the 
result of metabolic activity. When these compounds are 
acted upon by the enzymes, the end products or the interme- 
diate products formed may stimulate the formation of more of 
the enzyme, which in turn will lead to further disturbances. 
