SCHIZOMYCETES. BACTERIA 129 



Pruning during the growing season is also practiced, but it is less 

 reliable. Such pruning has not proven a great success on account 

 of the fact that infection may be constantly taking place. More- 

 over, when the blight is rapidly extending in a limb or trunk, it 

 is difficult to determine the extent of the region affected. In deal- 

 ing with this organism, in general, all possible bacteriological pre- 

 cautions must be taken. Carelessness in the pruning of nursery 

 stock may actually result in spreading the disease to practically 

 all of the young trees. The knife should be promptly applied 

 wherever a limb or trunk may be saved, and antiseptic precau- 

 tions should be taken. 



XI. WILT OF CUCURBITS 



Bacillus tracheiphilus Erw. Smith 



Smith, Erw. F. Bacillus tracheiphilus, sp. nov., die Ursache des Verwelkens 

 verschiedener Cucurbitaceen. Centrbl. f. Bakt., Parasitenk. u. Infektskr. 

 l(Abt. II): 364-373. 1895. 



The wilt of cucurbits was first reported about 1893 (Smith) and 

 it is now the most common and perhaps the most serious disease 

 among cucurbitaceous plants in the United States. It was at first 

 known (to pathologists at least) in the northeastern states, but it 

 is now common upon several hosts in Missouri, Colorado, and 

 other western states. Cucumbers and melons would seem to be 

 most susceptible, although pumpkins and squash may be attacked. 

 Weather conditions do not seem to affect materially the abun- 

 dance of this disease. 



Symptoms. The general symptoms are simple and striking. 

 These consist of a progressive wilting of the host. If infection 

 takes place upon the central stem, the wilting in the whole vine 

 follows promptly. If, however, infection is in the distal parts of 

 branches, there is gradual wilting back to the main stem. Then 

 the remaining branches promptly show the effect. In the tissues 

 there is at the time of wilting very slight, if any, evidence of a 

 change in appearance. In no case is there the development of 

 odors, or of decay in the usual sense. 



Infection and spread of the disease appears to result almost 

 wholly through biting insects. The organism is found massed 

 primarily in the vessels of the xylem. At first the spiral vessels 



