Contents xv 



PAGES 



cial light Monochromatic light Half-shade in plant 

 propagation Crops responding to half -shade Morpho- 

 genic effects Half-shade and quality The effect of shad- 

 ing upon other environmental factors Laboratory work 

 References 415-435 



CHAPTER XVIII 

 RELATION TO DELETERIOUS CHEMICAL AGENTS 



General relations to poisons Comparative resistance Toxic 

 action and the substratum Method of action Inorganic 

 and organic acids Alkalies Salts of the heavy metals 

 Formalin Organic bodies Root excretions Unproduc- 

 tiveness Relative toxicity of some organic compounds 

 Illuminating gas Stimulation by means of weak toxic 

 agents Protection of crops by insecticides and fungicides 



Destruction of weeds by poisons Deleterious substances 

 employed Practicability of the chemical method Labora- 

 tory work References 436-462 



CHAPTER XIX 

 VARIATION AND HEREDITY 



Variation: Individuals and species Fluctuating variations 

 Darwin's theory of natural selection Rate of increase 

 Fluctuating variation and the origin of varieties Pure lines 



Mutations Mutation and crop improvement . . 463-476 

 Heredity : Nonsexual reproduction and heredity Sexual repro- 

 duction and heredity The early studies Types of inherit- 

 ance Recent studies Mendel's experiments Purity of 



the gametes Results of segregation Tomato characters 



Chromosome relations Selection Laboratory work 

 References 476-493 



CHAPTER XX 

 GROWTH MOVEMENTS 



Stimulus and response Tropic curvatures Geotropism Thig- 

 motropism Chemotropism Nutation Nastic curvatures 

 Nyctitropism Laboratory work References. . 494-507 



