27 



with many leaves shading the surrounding soil, thus conserving 

 moisture and promoting quick growth. 



3. Abundavce of Insect Pests. The disease is chiefly spread by 

 means of infection from wounds, and under field conditions these are 

 usually produced by insects, especially the cabbage worm (Pieris 

 brassicae) which was very numerous upon cabbage and cauliflower 

 leaves. A careful examination of over 100 plants showed that one or 

 more larvae were present on each plant. Slugs also do considerable 

 damage to these plants, and obviously smear themselves with a number 

 of soil organisms, and as I have already mentioned, the Bacillus 

 olearaceae is probably a soil organism. 



Ants and other insects swarm around turnips, eating the rotted 

 pulp, and no doubt serve to carry the germs to other plants. 



4. Injury from Planting, Cultivation or Wind. Leaves of 

 turnips are frequently bruised or injured during cultivation, by either 

 hand or hotse hoes. Caulifioweis may be injured during planting- 

 out, and the infecting organism brought into contact with the broken 

 surface. In CHses of very rank growth, a heavy wind may cause 

 leaves to be broken off, and thus afford bacteria a cLance to penetrate 

 into the plant tissues. Many gardeners trim their cauliflowers on the 

 field, and when these are infected they carry the disease on to another 

 season. The same ground is often used year after year for the same 

 crops, a dangerous procedure when disease is present, as it is likely 

 to make the trouble endemic. 



5. Susceptibility of Vaiieties. According to the limitatijns 

 placed upon the meaning of " resistance " and " immunity " in plants 

 by Russell, we shall define ' resistance as the "inherent power of the 

 vegetable organism to withstand the action of bacteria in general ; " 

 and immunity as "the ability of the organism to repel the attacks of 

 a germ which produces a pathological condition in a closely allied 

 form." 



We find that white turnips and cauliflowers are very susceptible 

 to incculations of Bacillus oleraceae, whether carried out in the 

 laboratory, or met with under field conditions. Our laboratory 

 experiments were all carried out on the Greystone variety of white 

 turnips, which, under field conditions, seems to have some immunity ; 

 but which readily succumbs to artificial inoculations. We have kept 

 careful record of the amount of disease present among the different 

 varieties tested on our trial grounds. 



