FIELD STUDIES OF THE DISEASE. 47 



FUNGOUS INOCULATIONS. 



It has been supposed by some people that Pestalozzia and Diplodia 

 or Botryodiplodium })lay an important part in producing the disease, 

 since one or more forms of these organisms are found in abundance 

 on the central rotted leaves. Very frequently brown spots occur on 

 the middle of young leaves of trees which are apparently free from 

 bud-rot, i. e., which show an entire absence of a putrid condition 

 of the heart. These brown spots range from minute ones to those 

 5 centimeters in diameter, and they seldom become larger, but 

 remain in a dry condition, presenting the same appearance in the 

 older and mature leaves. Such spots are, without much doubt, 

 caused by both Pestalozzia and Diplodia, both of which form tiny 

 black pustules in the center of a diseased area. If, as has been said, 

 the spots remain dry, they seldom cause any serious damage to the 

 leaves. On the contrary, if bacteria also are present, causing a wet, 

 slimy condition, it is a beginning of the bud-rot. The bacteria 

 destroy the leaf tissues immediately under the epidermis, leaving an 

 extremely tliin, paperhke covering over the destroyed parenchyma 

 cells and the firm woody cells of the leaf veins. This condition 

 occurs frequently in an infected region. There may be but a half- 

 meter of diseased tissue, consisting of both a luxuriant, black, sooty 

 covering of the fungus and the slimy bacterial growth. This tissue 

 may be 1 to 1| meters below the top of the central leaves and as far 

 above the heart tissues. The sHmy condition progresses downward 

 into the more fleshy tissues, where it becomes a typical soft rot. The 

 advancing margin of tliis rot almost never contains fungous filaments 

 but swarms with bacteria and forms the typical bud-rot. The slimy 

 condition extends upward only so far as it may have fairly soft tissue 

 for food material, and is protected by surrounding leaves which 

 keep it constantly moist. Higher up in the crown where the leaves 

 begin to unfold the tissues are harder and more membranous and are 

 exposed to the wind and sunlight which furnish conditions unfavorable 

 to the growth of the bacteria. The fungous infection seldom extends 

 to the top of the diseased leaves, which turn brown and dry and supply 

 a poor substratum for the fungous growth. Under the foregoing con- 

 ditions, when both fungi and bacteria were present in incipient cases, 

 it was a puzzling question as to which was the cause of the diseased 

 condition. In a number of trees, however, the middle leaves were 

 affected with the fungous spots alone, and, as previously mentioned, 

 it may be seen that either fungi or bacteria may be the first present. 

 It is probable that germination and growth take place best in the 

 presence of unusually moist conditions among the tightly packed 

 middle leaves or on some of the frequent droppings of the tree frogs, 

 lizards, and various insects which are found present in such places. 



228 



