Contents xv 



PAGE3 



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- 

 Ileferences . . 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- 

 tivenessRelative 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 . 



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- 

 anceRecent studies Mendel's experiments Purity of 



the gametes Results of segregation Tomato characters 



Chromosome relations Selection Laboratory work - 

 References 



CHAPTER XX 

 GROWTH MOVEMENTS 



Stimulus and response Tropic curvatures Geotropisni- -Thig- 

 motropism Chemotropism - - Nutation Xastic curvatures 



Nyctitropism Laboratory work --References . . 494-507 



