796 EXPERIMENT STATION RECORD. 



the different varieties to disease. It is also stated that all varieties 

 of oats are comimratively resistant to rust until nearly the time of their 

 flowering. With 3 varieties of rust-resistant oats there was a com- 

 parative rustiness not to exceed 5 per cent for all dates of seeding. 



The difference in resistance is thought to be due in part at least to 

 structural differences. 



The Puccinia graminis is the variety of rust whicli first fails to 

 attack the resistant oats. P. coronata furnishes tiie earliest and most 

 persistent attack. 



The cause and prevention of pear blight, M. B. Waite ( U. S. 

 Dept. A(/r. Yearhoolc 1895^ pp. x"jj-300). — In a popular article the author 

 gives the results of a prolonged scientific investigation on the cause 

 and prevention of pear blight. The cause of the blight is Bacillus 

 aniylovorus and the life history of the organism has been worked out 

 very carefully by means of cultures and inoculations. The blight 

 attacks and rapidly kills the blossoms, young fruits, and new twig- 

 growth, from which it passes through the living bark to the larger limbs 

 and finally to the trunk. The parts of the tree that are killed by the 

 blight are the inner bark and cambium, and as a result the other i)arts 

 die. 



The infection takes place througli the flowers, and insects serve to 

 spread it from one cluster to another. The bacillus also gains entrance 

 through tips of growing shoots. This form, which is the usual one in 

 nurseries, is often called twig blight to distinguish it from the infection 

 through tlie flowers, but they are both due to the same cause. 



The conditions affecting the disease are numerous, and some of these 

 may be controlled by the grower. There is a great dift'erence in the 

 resistance of different varieties to disease, the Duchess and Keiffer 

 being less severely attacked than Bartlett and Clapp Favorite. Cli- 

 matic conditions influence the disease to a marked degree; warm, moist 

 conditions favoring, while dry, cool, sunny weather hinders and if pro- 

 tracted will check it entirely. The organism can not withstand drying 

 at all, but is able to survive a very considerable degree of cold. It is 

 carried over the winter in the tree to reappear in spring when the sap 

 has begun to flow. At this time the blighted areas may be recognized 

 by the moist and fresh appearance of the blighted bark, and a gummy 

 exudation flows out to be visited by bees, etc., by which the disease is 

 spread. 



The treatments for the jirevention of pear blight may be grouped 

 under 2 general heads: Methods which aim to put the tree in condition 

 to resist the disease, and those which are designed for the extermina- 

 tion of the bacillus. The methods under the first head must be directed 

 toward the prevention of rapid growth since vigorous growth increases 

 liability to disease. On this account pruning when the tree is dormant; 

 excessive fertilizing, especially with nitrogenous manures; and culti- 

 vation are to be avoided. Where irrigation is possible, withholding 

 water will greatly reduce the disease. 



