6 DEPARTMENT OF AGRICULTURE, BULS. 151-175. 



Page. 



Department Bulletin No. 169. — Injury by Disinfectants to Seeds and 

 R( m.ts in Sandy Soils: 



Introduction 1 



Soil characters % 1 



Experiments at Halsey, Nebr 2 



Experiments at Morrisville. Pa 30 



General discussion and conclusion 31 



Summary 34 



Department Bulletin No. 170. — The European Pine-shoot Moth; a 

 Serious Men-ace to Pine Timber ix America: 



Introduction 1 



Ilisti try of the species in Europe 2 



Food plants 3 



Introduction and distribution in America 4 



Life history 5 



Character of injury 6 



Description 7 



Allied American species 7 



Natural enemies 8 



Method of control 9 



Bibliography 10 



Department Bulletin No. 171. — Food of the Robins and Bluebirds of 

 the United States: 



Introduction 1 



Robin 2 



Varied thrush, or Oregon robin 16 



Eastern bluebird 19 



Western bluebird 25 



Mountain bluebird 29 



Department Bulletin No. 172. — The Varieties of Plums Derived from 

 Native American Species: 



Introduction 1 



Geographical origin of varieties 2 



Parentage of varieties 3 



Varieties classified by species 4 



Origin and species of native varieties of plums and of hybrids 8 



Department Bulletin No. 173. — The Life History and Habits of the 

 Pear Thrlps in California: 



Introduction 1 



History 3 



Economic importance 7 



Character of injury 11 



Description 19 



Systematic position 22 



Anatomy 22 



Life history and habits 24 



Natural enemies 51 



Department Bulletin No. 174. — Farm Experience with the Tractor: 



Introduction 1 



Designation of tractors 2 



Steam and gas tractors 3 



The gas tractor and the horse 4 



Tractor ratings 5 



Source of data 6 



Observations of business men 7 



Opinions of tractor owners 8 



Reports of satisfied and dissatisfied owners . . „ 10 



Gasoline and kerosene tractors 18 



Fuel supply 20 



Fuel consumption 21 



Lubricating oil 23 



Cross section of plows drawn and area plowed by tractors 23 



Breaking 24 



Combination work 25 



Depth of plowing 26 



