508 



BACTERIAL DISEASES OF PLANTS 



veloped shoots, the latter regularly produced, under stomata, 

 which were always wide open, small intumescences (hyperpla- 

 sias) in large numbers both on the stems and on the leaves (Figs. 

 400 to 404) . These intumescences were more abundant or rather 



more conspicuous at 28 to 35C. (Fig. 405) 

 than at 23 to 25C., but they occurred 

 also at the latter temperature (Figs. 406), 

 although on some parts of the shoots at 

 this temperature a microscopic examina- 

 tion was necessary to determine their pres- 

 ence (Fig. 407). The former were in bright 

 light, and the latter in the dark or rather 

 in very feeble diffused light, packed away 

 in quinine cans. The other conditions 

 were the same, viz., a wet base (the block 

 stood on very wet cotton or in water), 

 saturated air, diminishing oxygen and in- 

 creasing carbon dioxide. I am inclined 

 to think, in this case, therefore, that the 

 intumescences were due to excessive ab- 

 sorption of water, coupled with acid 

 stimuli liberated by a disturbed transpira- 

 tion, due to a saturated or nearly saturated 

 atmosphere. Of course, with temperatures 

 near the optimum for growth (as would be 

 the case in the top of a hothouse in bright 

 light) there would be a more conspicuous 

 development of such intumescences than at 

 lower temperatures in which growth is 

 much slower and in the latter it might re- 

 quire examination with the microscope to 

 demonstrate the beginnings of intumes- 

 cences. On the pared sterile blocks of 

 potato one of the most striking of these 

 tumors, which was narrowly pediceled and 

 covered with membrane, developed as a teratoma (Fig. 408). 

 In these various examples it will be observed that the cells 

 exhibit all grades of development from simple hypertrophy (Figs. 



FIG. 383. Cross- 

 section of a Vermont 

 tomato leaf showing 

 marked natural oedema. 

 Upper surface at left. 

 A few of the palisade 

 cells unchanged. (After 

 Atkinson.} 



