J. T. Wadsavorth 85 



(a) With Cabbages. 



The cabbages (variety Leeds Market) were planted out on May 1st 

 and the discs were placed in position on the following day. Altogether 

 816 cabbages were utilised for this experiment; they were planted in 

 eight rows, each row containing 102 plants : disced and undisced rows 

 alternating with each other. The spring was a particularly good 

 growing season and the plants made excellent growth. On June 18th, 

 some of the unprotected plants first showed signs of maggot attack and 

 on June 23rd a count of the plants was made. None of the protected 

 plants showed signs of attack but thirty-one of the unprotected plants 

 — -equal to 7-6 per cent. — exhibited the usual signs of severe infestation. 

 The attack was very evenly spread over each of the four undisced rows : 

 the numbers of attacked plants in each row being nine, seven, seven, 

 and eight respectively. 



On July 8th the cabbages were again counted when the percentage 

 of attack had increased to 1.3-2 ; fifty-four out of the total number of 408 

 unprotected plants being severely attacked, whilst only one of the 

 protected plants had succumbed to maggot attack, i.e. less than 0-25 

 per cent. 



Several of the infected plants were taken up for examination and in 

 all cases the original fibrous roots were absent, having been destroyed 

 by maggots; in some cases the latter were still feeding on the roots 

 and in those cases where they were absent pupae were present in the 

 surrounding soil. In many plants new fibrous roots were developing 

 near the upper portion of the main root and it was evident that the 

 attack caused by the first generation of flies was ended. 



The opinion of the market-gardener was that possibly one-third of 

 the infected plants would develop a fresh set of roots and recover from 

 the attack, although the resulting cabbages would be only small. 



On July 13th the plants w^ere counted again. No further attack was 

 evident; the cabbages were counted at intervals of seven days until 

 mid- August but no further losses were incurred. 



As only one plant was lost owing to maggot attack out of 408 plants 

 protected by the discs it is very strikingly evident that the latter afforded 

 a very complete protection to the plants. The protected cabbages were 

 also larger on the average and slightly earlier in coming to maturity than 

 those in the unprotected rows. A probable explanation of these differ- 

 ences will be mentioned when discussing the results of the cauliflower 

 trials. 



Ann. Biol, in 6 



