Introduction 5 



ditions upon the organism. The plant is a delicate physi- 

 cal, chemical, and living mechanism ; and through the 

 work which is performed, often expressed in growth, or 

 change of some sort, it is responsive to practically all 

 manner of stimuli. 



Under whatever conditions it may be able to grow and 

 reproduce itself there are many phenomena, or processes, 

 which are recognized as fundamentally physiological, al- 

 though the information respecting these may often be es- 

 sentially physical or chemical. All modern physiologists 

 are necessarily pursuing physico-chemical methods in in- 

 terpreting all the activities of plants. Among these pro- 

 cesses may be mentioned the absorption, movement, ' and 

 incorporation of water and of gases ; the absorption and 

 disposition of nutrient salts; the manufacture of organic 

 food material ; the accumulation, digestion, and assimila- 

 tion of foods or food materials ; respiration ; growth and 

 variability; reproduction and heredity; and the special 

 growth or other changes as responses to environmental 

 factors. Much of the material presented in this book is 

 for the purpose of demonstrating simply some of the essen- 

 tial principles involved. Qualitative measurements are 

 frequently sufficient. 



5. Environment. - The environment of any plant or 

 crop is a complex of factors or conditions as a resultant of 

 which there is the response of the plant in vigorous or 

 weakly production, and in diverse form or habit of growth. 

 Most of the important factors of the environment affecting 

 the agricultural plant are perfectly obvious. In consider- 

 ing these one almost unconsciously thinks of those factors 

 which operate above the soil and those which operate 



