44 



BACTERIAL DISEASES OF PLANTS 



Ai^disia plants, so far as I have been able to observe, grow 

 very slowly. Query: Are they dwarfed by the presence of the 

 bacteria, or on the contrary if deprived of them w^ould they be 

 unable to grow" at all? I set one of my assistants at work on 

 the problem, asking her to heat Ardisia seeds in water at tem- 

 peratures between the killing point of the seeds and that of the 

 bacteria (which is somewhat lower). The seeds heated for the 



Fig. 33.— Part of another leaf-nodule of Pavetta angustifolia (Fig. SO A) more 

 highly magnified, showing many small cavities. 



right time at the proper temperature were not killed but germi- 

 nated and grew, although with extreme slowness as compared 

 with those growing from untreated seed, so that even after a 

 year they had scarcely a leaf to show but only a swollen bud 

 and some roots. Sections from the leaf-teeth of such plants 

 showed them to be free from bacteria, and this makes it seem 

 probable that Ardisia plants actually require the bacteria. A 



