A Study on Gummosis of Prunus and Citrus, with 
Observations on Squamosis and Exanthema of 
the Citrus.! 
BY 
ORMOND BUTLER. 
With Plates VII-X and three Figures in the Text. 
PREFACE. 
HE studies which form the groundwork of the present memoir were 
begun during the autumn of 1907, under the direction of Professor 
R. E. Smith, at the Pathological Laboratory, Whittier, California, being later 
continued in Professor B. M. Duggar’s laboratory, Cornell University. 
The histological studies on gummosis were almost exclusively confined 
to the Czirus during my stay in Southern California. Having satisfied 
myself that the gum diseases of Prunus and Citrus were histologically 
similar maladies—in other words, confirméd the opinion held by Savastano 
in 1884—I attempted to trace out, using Mikosch’s recent memoir as a guide, 
the elusive first stages of gummosis, but only succeeded in reaching the 
decided opinion that this author’s views would not apply in the case of the 
Citrus. When, therefore, I transferred my work to Cornell University, 
I decided to reinvestigate gummosis in Prunus, as the results arrived at by 
Mikosch would bear confirmation, while, at the same time, continuing my 
histological studies on Cz¢rus. The present paper is the outcome of this 
combined study. a 
Gummosis is a fairly common phenomenon in the vegetable kingdom, 
but this malady, in other plants, has hardly been sufficiently studied to 
- warrant a comparative review in the present state of our knowledge. 
I have, however, devoted a few remarks to squamosis and exanthema 
of the Citrus, as these maladies have features common to gummosis, and 
have not, hitherto, been histologically described. 
In closing this preface it is my pleasant duty to acknowledge my 
indebtedness to Professor B. M. Duggar, and I know not how better to do 
so than by saying that it is far ee than could be told. 
O. B. 
June, 1910, 
§ Laboratory of Plant Physiology, Cornell University, Contribution No. I. 
[Annals of Botany, Vol. XXV. No. XCVII, January, 1911.) 
