CONTENTS. 



vu 



Bulletin 174 — concluded. page 



Digestibility of pumpkins, ....... 62-66 



Feeding experiments with pumpkins, ...... 66, 67 



Feeding pumpkins to milch cows at this station, . . . 67-71 



Bulletin 175. Mosaic disease of tobacco, ....... 73 



Introduction, ........... 73 



Historical summary, ......... 74 



Names, . . . . . . . ■ • . . .78 



Description of the mosaic disease of tobacco, ..... 78 



Occurrence, ........... 80 



Economic importance, . . . . . . . . .81 



Infectious nature of the disease, . . . . . . .81 



Contagious nature of the disease, ....... 82 



Pathological anatomy, . . . . . . . . .83 



Leaves, ........... 83 



Stems, 84 



Roots, 85 



Fungi and the mosaic disease, ........ 85 



Bacteria and the mosaic disease, ....... 86 



Dissemination agents, ......... 87 



Insects, ........... 87 



Workmen, ........... 88 



Seed, 89 



Fertilization in relation to mosaic disease, ...... 90 



Effect of colored light on mosaic disease, . . . . . .91 



Experimental data, ......... 93 



Biochemical studies, ......... 96 



Enzyme activities in healthy and diseased plants, . . . .96 



Reaction of mosaic sap with various substances, .... 105 



Probable character of the causal agent, . . . . . .110 



Prevention and control, . . . . . . . . .113 



Summary, . . . . . . . . . . .117 



Bulletin 176. The cause of the injurious effect of sulfate of ammonia when 



used as a fertilizer, . . . . . . . .119 



Part I., Chenaical investigations, ....... 119 



Part II., Water cultures 125 



Conclusions, ........... 134 



Bulletin 177. Potato plant lice and their control, ..... 135 



Economic importance of the pest, ....... 135 



Description of potato plant lice, ....... 136 



Manner of feeding and nature of injury, ...... 136 



Life cycle of the potato plant louse, ....... 137 



Control measures, .......... 138 



Practical considerations and fundamentals of control, . . . 138 



Efficiency of various contact insecticides for the control of potato lice, 139 

 Discussion of results, ......... 140 



"Black Leaf 40," 140 



"Black Leaf 40" and Pyrox, etc., ...... 141 



"Nico-Fume" liquid, ........ 141 



Fish-oil or whale-oil soaps, ........ 142 



Kerosene emulsion, ......... 142 



Miscible or soluble oils, ........ 143 



Lime-sulfur, .......... 143 



Spraying apparatus, ......... 143 



Summary of control measures, ........ 144 



Natural agents in the control of potato plant lice, .... 145 



Acknowledgments, .......... 146 



