Plants must gain from the environment the raw materials they need to sustain their structure, growth, and development. In Part I, we learned how they use light energy in photosynthesis and chemical energy generated through respiration to manufacture a wide array of organic chemical compounds. The focus in Part I was very much on the role of carbon from carbon dioxide in this endeavor. Part II is devoted to the question of what else plants need to sustain their growth and development.

In contrast to animals, the nutritional requirements of plants are simple. In addition to carbon dioxide, they need only water and certain chemical elements, all of which they most often take up from the soil. In the first two chapters in Part II, we examine how plants take in and distribute the water and mineral elements they require. The third chapter deals separately with the special case of how plants acquire and use nitrogen. A final chapter describes how plants transport substances of all kinds within and between their various organs.

These physiological processes are often grouped under the collective heading of plant nutrition.