697 



blood red bundles of the trunk. It has been proved by careful inoculation 

 experiments that the cause of the disease is Pseudomonas (Bacillus Cobb) 

 vascularum. 



Smith considers the red coloration of the branches (corresponding to 

 the brown coloration of bacterial gummoses) as a reaction of the plant. 

 According to Prinsen Geerlings, a neutral uncolored substance, dissolving 

 with difficulty, exists in the cellulose of the normal sugar cane, which turns 

 yellow with the action of an alkali (like tannin), but becomes red, when 

 aerated, and later brown. 



The interesting result is the definite proof that certain varieties of cane 

 (common green cane) in inoculation experiments show extraordinarily great 

 susceptibility, while other varieties (for example, common purple cane) 

 become only slightly diseased. The sap of the latter canes showed approxi- 

 mately a doubled acid content and Smith surmises that the high suscepti- 

 bility to parasites depends "only on the weak acidity or the minimal occur- 

 rence of a specific arresting acid." Cobb reports that where such resistant 

 varieties are grown the disease has disappeared. 



To the same group of diseases belongs also the disease of the sugar 

 beet which I first described as "bacterial gummosis" and later as "beet tail 

 rot.""*- So far as can be determined experimentally, the bacteria have an 

 epidemic distribution only if continued heat and drought with abundant 

 nitrogen fertilization weaken the growth of the beets. If wet weather 

 sets in with the same excessive fertilization, the yield in sugar becomes 

 considerably less, but the bacterial gummosis is lacking\ 



Peach Yellows. 



Since 1887 a disease of the peaches in the United States of North 

 America has been studied very earnestly. It has caused uncommonly great 

 injury to extensive orchards. A yellow disease (chlorosis) is concerned 

 here which is transmissible by grafting-. This condition of yellow foliage 

 differs in this from the similar phenomena caused by a lack of nutrition, 

 frosts, etc. In this disease, which has constantly increased in the last 20 

 years and has made the cultivation of the peach unprofitable in many places 

 (in the Delaware and Chesapeake regions), a peculiar red mottled condition 

 and a premature ripening of the fruit are very characteristic. To this 

 should be added the premature development of the winter buds and the 

 extensive development of latent and adventitious buds; therefore, a diseased 

 branch as in the Sereh disease. Although the fruit, which at times has red 

 stripes extending into the flesh, attains a normal size in the first year, it 

 becomes smaller in the following years of the disease, and tasteless, or even 

 bitter. The phenomenon is restricted at first to a few branches and then 



* See V. 2 of the Manual, p. 42. 



1 Zeitschr. f. Pflanzenkrankh. 1S92, p. 2S0. 1S96, p. 296, and 1S97, p. 06. Blatter 

 ■ f. Zuckerrubenbau 1S94, p. 1. 



- Smith, E. F., in Report of the chief of the Section of Veg-etable Pathology. 

 Washing-ton, 1890. Smith, Erwin F. Additional evidence on the communicability 

 of peach yellows and peach rosette. Washington 1891, Bull. 1. 



