10 BACTERIAL DISEASES OF PLANTS 



leading to non-susceptibility occur in the Japanese plum sub- 

 ject to Bacterium pruni; the young fruits are very susceptible, 

 the maturing fruits cannot be infected. In the destructive 

 coconut bud-rot of the West Indies (Fig. 4) only the young 

 "swords" and the undeveloped, sheathed, terminal bud are 

 attacked by the bacteria. 



Other parasites, on the contrary, are able to attack, disin- 

 tegrate and destroy matured tissues, such as the pith of cabbage 

 stems, turnip roots, the ripened tubers of the potato, the well-de- 

 veloped roots of sugar beets and of carrots, the bulbs of onions 

 and hyacinths, full-grown melon and cucumber fruits. 



In both of these types the action of the parasite is expended 

 chiefly on the parenchyma. Although in some cases (the plum 

 disease, Appel's potato rot) there is more or less bacterial in- 

 vasion of the local vessels, vascular occupation is not a special 

 characteristic. 



In the typical vascular diseases the case is reversed. Here 

 parenchyma is also destroyed, more or less, but the most con- 

 spicuous and destructive action is on the vascular bundles, 

 the hadrome vessels of which are occupied for long distances, 

 to the death, or great detriment, of the whole plant. In maize 

 attacked by Aplanobacter stewarti, it is not unusual, indeed one 

 might rather say it is customary, to find the vessels of the stem 

 filled with the bacteria continuously for a distance of 3 to 6 

 feet from the point of infection, i.e., from the surface of the earth 

 to the top of the full-grown plant. In cucurbits attacked by 

 Bacillus tracheiphilus, in bananas attacked by Bacillus musae 

 (Fig. 5) and in sugar-cane attacked by Bacterium vascularum the 

 same thing occurs, and many of the vessels are filled solid with 

 the bacterial slime to a distance of 8 or 10 feet from the place of 

 infection. In such cases infection has taken place, generally, 

 near the base of the plant which continues to grow for some 

 weeks or months. 



Transitions, of course, occur. For example, Aplanobacter 

 stewarti, is confined much more strictly to the vascular bundles 

 of the maize stem than is Bacteriwn solanacearwn to those of 

 the tomato, potato, or tobacco stem, although it also is a vascu- 

 lar parasite ; that is, following infection of the vessels we do not 



