172 



BACTERIA IN RELATION TO PLANT DISEASES. 



into the parenchyma filling the interior of certain of these cells, while at other times they 

 occupy only the intercellular spaces and wedge apart the parenchyma cells to form cavities. 

 Fig. 80 b shows Bacillus musae filling one of the spiral vessels of a bundle. 



Fig. 80.* 



THE PANAMA DISEASE. 



In 1904, Dr. R. E. B. McKenney discovered a banana disease in Central America 

 which had destroyed whole fields and which threatened to destroy the industry over large 

 areas. During the next 4 years he found the disease on every banana farm in Costa Rica, 

 meaning by this every plantation where bananas are grown in quantity for market. He also 

 observed the disease as far south as the canal region of Panama, and from reports made to 

 him he believes that it occurs as far north as British Honduras. The disease has probably 

 existed in Central America for a long time, but has been destructive only within the last 10 

 years. During this time many large fields of bananas belonging to the United Fruit Com- 

 pany have been entirely destroyed. Up to the summer of 1909 he believed the disease to 

 be of bacterial origin, and thought that he had some evidence of this from pure-culture inocu- 

 lations made in Costa Rica. But inoculations made in the hot-houses of the U. S. Depart- 

 ment of Agriculture with his bacterial cultures have yielded only negative results. This 

 disease first attacks portions of the rhizome. The rhizome is so large, however, that many 

 months usually elapse before the whole of it is destroyed. The most conspicuous signs of 

 this disease are: first, the yellowing of the leaves; then the sudden wilting and shriveling 

 of the entire foliage. The rhizome now sends up new shoots, which appear to be healthy 

 at first, but after a time these also perish with the same signs. In a badly diseased field 

 one sees very few tall banana plants, but multitudes of low shoots, healthy or in various 

 stages of the disease. When the banana leaves are full grown, or nearly so, the signs are 

 yellowing and wilting. In younger leaves the yellowing, which begins at the terminal 

 portion, is accompanied by the downward curvature of the apical 2 to 3 feet of the leaf 

 in a peculiar and characteristic manner. 



*FiG. So. A. Longitudinal section of spiral vessel of a banana bundle attacked by Smith's Cuban disease. Petiole 

 sound externally. Section 7 feet 4 inches below point of inoculation. Bundle browned and occupied sparingly by 

 Fusarium cubense, which is producing internal conidia. Section drawn after being cleared in 10 per cent potash over 

 night. Inoculations of 1909. For comparison with B. 



B. Longitudinal section of banana fruit-stalk (fig. 76) showing two spiral vessels of a bundle: One occupied by 

 Bacillus musae, the other empty. Rorer's Trinidad disease. 



