DISEASES OF PLANTS. 705 



Experiments witli the woolly apliis show that the disease may be spread 

 by insects to the roots of seedling apples. 



A form of disease somewhat similar to crowu knot, but confined 

 entirely to the trunk and larger branches, is called by the author trunk 

 kernel, and is brielly described. The injui-y which it produces seems to 

 be confined to the roughening of the bark. 



A twig knot of quinces, which is frequently mistaken for crown knot, 

 is briefly mentioned. It is said to be a normal state of certain varieties. 



The disease called powdery bark is said to be quite common in Cali- 

 fornia. It is characterized by the drying up and cracking of the outer 

 bark, exposing a layer of the inner tissue which readily breaks up 

 into a fine pawder. Beneath this powdery layer the bark may be either 

 normal or dead. In case the bark is destroyed the branch usually dies 

 also. 



The gam disease of citrus trees is said to be one of the more serious 

 troubles connected with citrns growing in many localities. It is con- 

 sidered to be of parasitic origin, although apparently not due to any par- 

 ticular organism but rather the combined action of several. Two forms 

 are recognized, one originating at or near the crown and the other 

 attacking the deeper parts of the roots. The latter form is also called 

 root rot or foot rot and appears practically uncontrollable. Avhile the 

 former is said to be easily cured. The disease is said to originate only 

 under unusual conditions of moisture and the presence of dead and 

 decaying organic substances, it being only possible for the organism to 

 enter a healthy tree through the intervention of decaying tissue. The 

 remedy is to remove diseased tissues and keep the place exposed to the 

 air and the tree will heal itself. 



A brief note is given on the gum disease of stone fruit, which is a 

 result of various causes, one of the most common being the attacks of 

 one of the toadstool fungi. This disease seems to be uncontrollable. 

 It is most prevalent in oak clearings, and generally a replanted tree 

 will take the disease. The removal of a large amount of earth, lining 

 the hole with iron or copper sulphate, filling it with new earth, and 

 replanting has been accompanied by good results. 



Sour sap and blight or die-back are considered of bacterial origin, 

 and vigorous pruning and the use of fungicides are recommended as 

 probably efficient means for their prevention. 



Leaf curl of peach is briefly described, for which washes composed 

 of lime, salt, and sulphur have been claimed to be efficient i)reventives. 

 These and other washes were tested at the station with negative results. 

 The use of winter washes, pruning, and summer treatment with Bor- 

 deaux mixture are recommended as probable means for keeping this 

 disease in check. 



The scab of apples and pears is briefly mentioned, and the use of 

 Bordeaux mixture recommended for its prevention. 



