236 AGRICULTURAL EXPERIMENT STATION. [Jan. 



it has been found that they are quite incapable of attacking 

 any of the living tissues of the host. They have been sown 

 on sound and on injured leaves, and on stems of various 

 ages, on those of the season and those of one, two and more 

 years old. Whether sown on the intact surface of the stem, 

 or allowed free access to the freshly exposed living tissues 

 of the inner bark (Phloem), the results have been the same. 

 No development of knots has followed any of the sowings, 

 nor has any trace of mycelial threads been found in the 

 tissues exposed to them. It seems pretty certain, then, 

 that they play no important part in the spread of the fungus. 

 Prevention. — Since we do not yet know the details of the 

 infection of the host-plant l)y this fungus, we are not in a 

 position to use fungicides intelligently. It is doul)tless true 

 that spraying at intervals during the w^hole period of the 

 ripening and escape of l)oth winter and summer spores, 

 namely, from January to June, will largely prevent the 

 attacks of this disease. But it is hardly less to be doubted 

 that a complete filling of this important blank in the life 

 history of the fungus will enable us to reduce the period of 

 spraying to a relatively short one. On the other hand, I 

 am convinced that the disease can be largely controlled with- 

 out spraying, if fruit growers will learn to recognize its 

 earliest appearance. The great difficulty at present lies in 

 the fact that a few small knots, even when fully grown, often 

 escape notice, and so serve as sources of infection ; and 

 indeed, the average man does not realize that his trees need 

 attention and that the fungus is getting the better of them 

 until they are so covered with knots as to be practically 

 worthless. While, as for the early stages of the knot, before 

 either of the spore forms have developed, no one thinks of 

 looking for them and removing them when removal is of 

 some avail. It is very rarely that a tree is badly attacked 

 the first season. Commoidy the beginning is the a})pearance 

 of one or two sniitil knots, of very little consequence alone, 

 but sufficient to infect the whole tree in two or three years, 

 if left. After a very little ex})erience any one can recognize 

 the forming knot even before it bursts the bark, and before 

 it has done serious mischief. No one would mistake the 

 large knot on the middle branch in PI. V. ; but it has 



