86 BACTERIA IN RELATION TO PLANT DISEASES. 



Spegazzini states that of the two common sorts of cane planted, Cafia rayada and Cana 

 morada, the former appears to be more subject to the disease than the latter. He also had 

 opportunity to examine some small plantations of Cana India and Cana Espanola or blan- 

 quita. He found the India free from the gangrene, whereas the Spanish was attacked by it. 



The planters sometimes reported that cane which had been attacked recovered there- 

 from, and this is sometimes true of individual plants, but not for whole localities. I quote 

 as follows : 



During my study I observed successively that the disease is permanent, and that if the cane 

 which is diseased does not die, which does not happen often, whether it be by keeping the vegetative 

 cone still healthy, or by throwing out lateral shoots, it always retains plainly visible indications of the 

 disease. 



In another place he makes the following statement in support of his view that the infec- 

 tion is centripetal, i. e., attacks first the external organs and then the internal organs: 



I will cite the recovery of diseased plants, a thing which all the cane growers are familiar with, 

 and who express it by the saying "the cane conquers the Polvillo. " 



The general effect of the disease on the plant is to make it grow slowly and develop its 

 leaves very, very slowly. On cutting cross-sections of diseased leaf-blades for microscopic 

 examination it was found that the gumminess was associated with a ' 'great number of cor- 

 puscles which appeared to be cocobacteria, mixed with bacilli and with mycelial threads." 

 Similar observations were made on the leaf-sheaths. An examination of the undeveloped 

 gummy leaves, including the terminal bud, showed a similar condition. I translate as follows: 



When these leaves become diseased the epidermis almost disappears, and the parenchyma is dis- 

 organized ; a yellow gum fills all the cells, and in this is found the protoplasm emulsionized, mixed with 

 countless cocobacteria, bacilli and mycelial threads. When the disease is very advanced, one finds 

 still entire only the woody vessels, which appear as threads or filaments. 



If the terminal bud is not killed outright it continues to develop "between dead or partially dead 

 leaf-sheaths which envelop the cane, almost strangling and suffocating it ; but it presents evidence of 

 the struggle, appearing etiolated and whitish and wrinkled, sometimes doubled over itself, bearing 

 almost always a sheath or skin-like covering of a dirty color, and with a peculiar fetid odor : the 

 remains of the new leaves which have died and which adhere to it still. 



Spegazzini examined the cane fields very carefully with reference to the possibility of 

 the disease being due to animal parasites. He mentions seriatim the forms found, such as 

 eel-worms, acarids, mites, sand-fleas, earwigs, Hemiptera, Diptera, and Lepidoptera of vari- 

 ous kinds, but comes to the conclusion that none of these are connected in any way etio- 

 logically with the disease, although possibly some of them may act as carriers. In the same 

 way he excluded all atmospheric conditions, soil conditions, and special methods of culture, 

 and came to the conclusion that the disease could be due only to bacteria. He states 

 that from the first samples, which had been long in transit, he isolated about fifty species of 

 fungi and bacteria, two of which were much more common than the others and therefore sus- 

 pected. On visiting the cane plantations he collected numerous samples of diseased canes, 

 isolating the organisms found in them by cultural methods, but only after much difficulty, 

 and again found these two species extremely common. 



The conclusions reached by means of these cultures are the following: 



(a) In the whole organ attacked by the Polvillo there exists a bacterium of form and characters 

 clearly defined. 



(b) In the parts, from the time diseased, there appears constantly a fungus in its various meta- 

 genetic stages, but of saprophytic characters. 



The bacillus is said to be a new species and is named Bacillus sacchari.* The fungus 

 was identified as Melanospora globosa Berlese. This occurs also on cane not diseased by the 

 wet gangrene. 



*This name is to be rejected on account of the earlier Bacillus sacchari Janse (1891). 



