1917] 
FREIBERG—MOSAIC DISEASES 221 
so because of the complexity of these reactions and, further- 
more, because of our ignorance of such things in the vegetable 
kingdom. The writer does not wish it to be thought that 
in drawing upon animal pathology for examples, an oppor- 
tunity is sought for begging the question of the production 
of the mosaic enzyme in infected plants. It merely serves to 
illustrate the fact that the production of the mosaic enzyme 
is no more complex than the production of toxins, serums, 
and the like in animal pathology, all of which are accounted 
for on physiological grounds. 
In the light of all evidence now at hand, we must consider 
the infective principle of mosaic diseases as being an enzyme, 
and in doing so we do not abuse any of our fundamental bio- 
logical conceptions of pathology and physiology. 
SUMMARY 
The evidence that has accumulated from the efforts of 
recent workers on mosaie diseases and that presented in this 
paper enable us to formulate the following summary: 
1. Mosaic diseases are not caused by an unbalanced 
inorganic nutrition. The inorganic elements are present 
in diseased and healthy tissue in relatively the same 
amounts. 
2. Carbohydrates are more abundant in the dark 
green than in the light green areas, regardless of the 
time of day. 
3. Proteins are present in both the lighter and darker 
areas. Preliminary nitrogen analyses indicate that the 
quantity of protein in the lighter areas is slightly in 
excess of that in the darker areas. 
4. Whether or not the disease is initially due to 
physiological disturbances or to parasites, the physio- 
logical phase is an extremely important one. 
5. Preliminary observations on temperature relations 
indicate that thére is not only an optimum for the mani- 
festation of the disease, but also a maximum and mini- 
mum above and below which the disease is checked. The 
