STUDIES IN THE MOSAIC DISEASES OF PLANTS 
GEORGE W. FREIBERG 
Research Assistant to the Missouri Botanical Garden 
The particular group of diseases commonly known as 
‘physiological’? diseases has occupied the attention of bot- 
anists — pathologists and physiologists — for Ше last forty 
years, but it is doubtful whether the interest has ever been 
as keen as that which has been evidenced through the investi- 
gations and reports of the last few years. 
Probably the commonest of the physiological diseases and 
the most studied, at least from the standpoint of the number 
of scientists whose attention it has occupied, is the one most 
generally known as the mosaic disease. The discovery of 
the disease, its appearance, and the results of the early in- 
vestigators have been adequately reviewed in recent publica- 
tions, while its occurrence on new hosts has furnished the 
subject matter of a number of short articles which have ap- 
peared recently. The object of this paper is primarily that 
of reporting the results obtained from experiments on mosaic 
diseases, but an attempt will also be made to review the ob- 
servations and results of the early workers, with a view of 
interpreting them in the light of the results of recent investi- 
gations, and above all, to consider all evidence now known on 
the basis of the fundamental principles of physiology and 
pathology with the hope of arriving at a clearer conception 
of the cause and nature of mosaic diseases. 
The most striking character is the differentiation of the 
green tissue of the blade into lighter diseased and darker 
apparently healthy areas. This naturally implies a differ- 
ence in the chemical composition of the tissue and suggested 
a microchemical study of the differentiated areas of the dis- 
eased leaves. It was hoped that the chemical differences ex- 
hibited between sharply defined areas might furnish a clue to 
the cause of the anatomical and histological differentiations. 
ANN, Мо. Вот. GARD., VOL. 4, 1917 (175) 
