PLANT DISEASES AND FUNGI. 25 



disease is really due to the microbe mentioned the malady differs 

 widely from that of any heretofore described bacterial injury to 

 living vegetation. The microbe must be sparsely but widely dis- 

 tributed through the still living tissues of the tree, in which it must 

 very slowly develop without causing evident local disturbance. This 

 latter especially is entirely at variance with known effects of parasitic 

 organisms. But we know that the peach tree affected with this 

 disease very gradually succumbs, lingering along several years with- 

 out iocal injury of pronounced type."" 



On the subject of the California vine disease, Mr. Pierce, a 

 special agent sent to investigate the disease, states that yellow spots 

 occur on the leaves, which showed no trace of insects or fungi. 

 That " the peculiar appearance and location of these spots led to a 

 careful study of the same, which resulted in finding bacteria-like 

 bodies in large numbers, within the chlorophyllose cells of the spongy 

 parenchyma immediately surrounding the spiral vessels supplying that 

 region. After a long series of observations, made on material from 

 various portions of the diseased district, which in no case failed to 

 disclose the diseased vines as swarming with these bodies in all 

 portions where sap had a ready flow, he believed it proper to under- 

 take a series of experiments to determine if these bodies, always 

 present, bore any relation to the disease as a whole. He had little 

 doubt that they were micro-organisms, and gave to the local spotting 

 of the leaves their characteristically sharp outline. Cultures from 

 various parts of the vine were made in agar-agar, and other media. 

 Three sorts of bacteria were found with enough constancy to warrant 

 further study, but he had not, so far, been able to determine whether 

 any of these were the cause of the disease. In view of the fact that 

 several Italian students have for years claimed that an Italian disease 

 of similar characteristics is caused by bacteria, it is proper the 

 matter should be decided, if possible."^ 



It is established, then, beyond doubt, that bacteria inhabit the 

 tissues of plants in great numbers, that they appear to be of kinds 

 peculiar to those plants, and may, or may not, be the cause of some 

 of the plant diseases. To carry on the subject still further, we must 

 refer to a series of investigations on a disease of melons, and, by 

 the results of these investigations, exhibit a very strong presumption 

 that microbes are the cause of some diseases of plants. 



6 " Report of the Secretary of Agriculture," U.S. Section of Vegetable Pathology for 1889, 

 P- 4-'3- 



7 Report for 1889, p. 427. 



