79 



sulphur shows 34.4 gain for Orchard I in 1907, on a plot the original 

 infestation of which was 8.8 degrees, and a gain of 39.4 percent in 

 Orchard II in 1911 ^.a a plot the original infestation of which was 

 8.2 degrees. It is true that the Rex plots in Orchard II agree less 

 closely in the two years, the 39.4 percent of 1911 being matched by 

 :i gain of 49 percent in 1907 ; but a glance at the grades of infesta- 

 tion explains the discrepancy, the 1907 plot having an average grade 

 before treatment of 3.1 degrees, and the 1911 plot a grade of 8.20 

 degrees. We get a more obvious improvement, as a general rule, 

 where the average infestation is the less. 



Summary 



1. Experiments with infested ripe apples show that the San 

 Jose scale may live and reproduce freely on such fruits plucked from 

 the tree and kept at ordinary room temperatures, and that living 

 young may continue to be born under such conditions during a period 

 of eight weeks. Infested apples taken from cold storage in December 

 gave similar results, young being produced on these apples for twenty- 

 five days. 



2. Exact breeding experiments conducted at Urbana in 1906, in 

 a way to distinguish thruout the season the descendants of the first- 

 born from those of the last-born of each generation, gave two suc- 

 cessive generations of the last-born series, in the complete year, and 

 four such generations of the first-born series. A computation based 

 on data thus obtained yielded a possible rate of multiplication under 

 optimum conditions of 32,791,472 to 1 for the year. This total is 

 only the 98th part of that of other investigators, who took no ac- 

 count of diminished numbers of generations produced by late-born 

 individuals. 



3. Spraying operations with various preparations of Hme and 

 sulphur and with two brands of miscible oils justify the usual pref- 

 erence for the sulphur solutions, especially because of their more 

 prolonged efifect when applied in spring. The home-made solutions 

 were equally effective with those ready-made and requiring only 

 dilution for use. These experiments also illustrate the great advan- 

 tage of early spraying, before an orchard becomes heavily infested, 

 and furnish evidence that spraying in spring is much more effective 

 than spraying in fall, the ratios of benefit being some 20 percent 

 greater. The possibility of redeeming and restoring a badly infested 

 orchard and maintaining it in good condition with one or two spray- 

 ings a year, was well established by these operations, 



