264 PLANT-BREEDING 



for the attacks of some dreaded disease. For the sooner the 

 time of sensibility is over, the smaller will be the harm 

 and the larger the number of uninjured thriving plants. 

 Experiments have been made in tliis direction in Sweden 

 on the resistance of grains against the devastations of the 

 frit-fly (Oscinis frit). This is a httle black insect, attaining 

 a length of only 2 or 3 mm. and easily recognizable by its 

 metalUc brightness, black legs, and yellow feet. It invades 

 the grains chiefly during the germination period, depositing 

 its eggs on the young plants. The larvag creep along the 

 leaves and their sheaths downward until they reach the young 

 halms, and in eating these they destroy the germ of all further 

 development. Some of the seedHngs may die shortly after- 

 wards, others may show signs of Hfe during some time, but 

 their growth is abnormal and for the harvest they are wholly 

 lost. Whole fields of all kinds of cereals may be destroyed 

 by this calamity during some few weeks. 



One of the best means against the attack of these flies is 

 the passing of the dangerous period of Hfe as rapidly as 

 possible. As soon as the young halms are old enough to 

 resist the invasion, the insects become nearly harmless. On 

 the basis of our considerations concerning the correlation 

 of the size of the seeds with the rapidity and simultaneous- 

 ness of the germination, we may therefore expect that the 

 sowing of selected large seeds or of large-seeded varieties 

 vdll give the desired protection. This is exactly the result 

 of the Swedish experiments. Nilsson and his staff made 

 comparative sowings of large and of small seeds separated 

 from one another by sifting, or even by simply choosing the 

 upper kernels of each spikelet for one trial, and the under 

 kernels, which as a rule are larger, for the other. By this 

 method all varietal differences were excluded and the result 

 was for oats, that the loss from the attacks of the flv was 

 small for the large seeds, but very notable among the smaller, 



