478 



BACTERIAL DISEASES OF PLANTS 



of the bacteria. This is also suggested by the fact that vessel- 

 ingrowths in great numbers may be produced in the absence of 

 parasites, by purely chemical means. The most striking ex- 

 hibition of tyloses I have ever seen, a veritable pseudo-paren- 

 chyma, was obtained in 1914-1915 by Caroline Rumbold in 

 the vessels of chestnut wood, by injecting a I SQQ g.m. solu- 

 tion of lithium carbonate (Fig. 357 to 359). Here the effect 

 was quite local both in time and place and there were other 

 surprising phenomena, viz., the appearance in the bark of 



FIG. 357. Cross-section of chestnut wood, spring of 1914, showing large 

 vessels filled with tyloses. Cut in 1915. Below is urraffected autumn wood of 1913. 

 From Caroline Rumbold's chestnut bark injections of spring of 1914 using J-oo 

 g.m. LioCOs. Photograph by the writer November, 1916. 16 mm.. 4 oc.. bellows 

 at 35. Reduced y%. 



numerous well-developed islands of wood, causing it to bulge 

 out (Figs. 360, sub. 6 to 362) while in the normal situation in 

 1915 much less than the usual amount of wood was produced 

 (Fig. 360 at 3). We may suppose the stimulus to have been 

 either the alkali, an excess of carbon dioxide liberated from it, or 

 both acting together. The same curious phenomenon enorm- 

 ous thickening of the bark (from 1 cm. to 5 or 10 cm.) with form- 

 ation in it of numerous islands of wood occurs in the brown bast 

 disease of rubber trees (Hevea brasiliensis] in the Dutch 'East 



