LEAF NODULES 



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it is infected through the stomata. From the growing point 

 the ovary and the seeds are infected, the latter through 

 the micropyle. In the seeds the bacterium lives between 

 the embryo and the endosperm, and infects the growing 

 point anew as the seed germinates. It was found possible 

 to sterilise the seeds by careful heating, and on the sterile 

 plants which were obtained no galls appeared. Such 

 plants grown in nitrogen-free soils gave very poor 



Fig. 36. — Bacterial nodules on leaves, i, Pavetta Zimniermanniatia, 

 showing nodules along mid-rib. | nat. size. 2, Infection of leaf of 



Psychotria through stoma, and dissolution of leaf cells. 

 Faber.) 



X 620. (After 



growth compared with infected plants. Faber isolated 

 the symbiont, showed that it could fix free nitrogen, and 

 that sterile plants infected with the cultures produced normal 

 galls and normal growth (Fig. 36). 



The picture presented by Ardisia crispa is less clear. 

 The bacterium again occurs at the vegetative point, and 

 again invades the leaves, the ovary, and the seeds, thus 



