184 Studies in Bacteriosis 



INCIDENCE OF THE DISEASE. 



Sometimes, during the first years of a nursery, plants have shown a 

 considerable amount of disease, but this has gradually diminished until 

 only a small percentage of the plants have been attacked in the later 

 years. Conversely, cases are known where ".Stripe" has appeared and 

 gradually increased after some ten or twelve years during which time 

 no sign of the disease has been observed. These facts would seem to 

 indicate the soil as the Jiiain source of infection a)id Howitt and iStone(-) 

 have shown that plants grown in soil from an infected house developed the 

 disease while plants grown in the same soil previously sterilised remained 

 free. The disease may appear in the seed-boxes, producing rapid destruc- 

 tion of tlie young plants and compelling fresh sowings to be made; it is 

 not uncommon to find the first symptoms of disease while the young 

 plants are still in the small pots (sixties) or again after these have been 

 planted out in the houses for a fortnight or so. Usually, however, the 

 disease first appears about May, when the earliest fruit is ready for 

 picking, but frequently no signs appear until the tops are allowed to 

 develop, when these often become badly attacked. 



There is a distinct connection between soft and rapid growth and the 

 incidence of disease, plants growing rapidly in the early stages are more 

 liable to "Stripe" than others of a hardier nature. In one case observed 

 at Cheshunt the plants were so badly attacked that it seemed impossible 

 for the crop to recover, the conditions were then altered so as to induce 

 a slower rate of growth with the result that the plants completely "grew 

 out of" the "striped" condition, showed perfectly clean tops and 

 yielded a good crop of sound fruit. 



OBSERVATIONS ON THE EXPERIMENTAL PLOTS. 



During the past season observations have been made on the inanurial 

 plots in the houses at C^heshunt to ascertain the relation of manurial 

 treatment to the incidence of the disease. The indications are that a soft 

 rapid growth such as is produced by excess of nitrogen and a high 

 temperature accompanied by damping renders tlie plant more suscep- 

 tible to stripe than does a hard slow growth accompanied by suitable 

 additions of potash. 



These observations arc fully conHrnicd by inoculation tests carried 

 out on plants grown in pots, the results of which will be found under 

 the heading "Inoculation Experiments." 



