8. a. Jones -ifUt 



would be attended by a collajjsing of the cells, so that access of air 

 through the diseased core would be prevented and thus hinder atmo- 

 spheric oxidation. At the time of infection in the field, the plants would 

 be actively growing and drawing upon the minerals in the soil. It is 

 conceivable that one or more of these substances would have an oxidizing 

 efiect on the bacterial .secretions in the diseased tissues, causing a dis- 

 coloration at the margin of the diseased area. E. F. Smith states that 

 Laurent, experimenting with different fertihzers on potatoes upon plots 

 which had been treated with sodium nitrate and sulphate of ammonia 

 produced tubers, which when inocidated with an organism (beheved to 

 be B. coli) gave a " black zone between the attacked and healthy tissues. 

 As this stain was not noticed elsewhere, Laurent attributed it to the 

 nitrogenous product formed by the bacteria at the expense of the 

 tissues." 



Relation of Parasite to Ho.st. 



The relation of the organisms to the tissues of the host was first 

 determined by examination of the diseased pulp of the field plant. 

 A small quantity of the pulp mounted on a slide and gently pressed down 

 with the cover-glass showed the cells to be completely isolated. The 

 cell-walls were, however, intact and presented no appearance of being 

 swollen. Numerous reticulated vascular strands were also seen with 

 their walled prosenchymatous elements attached in places. The bacteria 

 were generally seen outside the cells, but a few cells were so completely 

 occupied by them that they appeared black amongst the contiguous 

 imoccupied cells. Examination of the diseased pidp of inoculated plants 

 showed exactly the same phenomena. Such densely occupied cells with 

 the contiguous cells containing few or no bacteria were also seen in the 

 microtomed sections of inoculated material. 



Field material was fixed in Flemming's solution and in Carnoy's 

 acetic-alcohol. Small pieces of the diseased roots were cut to include 

 the healthy tissue, the brown zone, and the loose \)\\\\). The shdes made 

 from the material fixed in the Flemming mixture showed almost the 

 complete loss of the soft pulp in the prolonged process of washing. The 

 alcohol-fixed material was therefore employed. The pieces selected for 

 paraffin embedding included all the tissues from the periphery to the 

 soft pulp. Transverse and longitudinal sections were cut on the micro- 

 tome to a thickness of 4fi and mounted on shdes thinly coated with 

 white of egg. Considerable difficult}' was experienced in the differential 

 staining of the tissues and the bacteria respectively. The organisms 



