HOW PLANTS FEED AND GROW 33 



36. The proteins. Most of the protein is usually made by the 

 time the plant comes into blossom, and is located in the stem 

 and leaves where it was made ; but much of it is usually trans- 

 ferred to the fruit or seeds as they develop. Therefore the seeds 

 and fruit are richer in protein than are the straws and hays. 

 A familiar example of vegetable protein is the gluten in wheat. 

 Protein is composed principally of nitrogen, carbon, hydrogen, 

 and oxygen. Some proteins also contain sulphur, and others 

 phosphorus. Proteins are the most complex plant substances 

 known. While the amount of protein contained in most plants 

 is small in comparison with the amount of carbohydrates, it is 

 very important because, together with the mineral elements of 

 plants, it is the source of the growth of all animals. Without 

 protein, animals could not grow. 



QUESTIONS AND PROBLEMS 



1. What factors determine the abundance of the harvest, and how and 

 to what extent may man control each ? 



2. Give illustrations of farm crops which have been introduced into 

 new climates, and show the results which followed. 



3. Why is it important to plant a large piece instead of a small piece 

 of potato ? 



4. What are the relative advantages of planting four small pieces or 

 two large pieces of potatoes in one hill ? 



5. What percentage of the whole green corn plant does each group of 

 component substances form ? How may this be determined ? 



6. What are the necessary elements of plant food, and what are their 

 sources ? 



7. Assuming that the corn plant is a machine which manufactures and 

 uses food material, describe the machine, the sources of the materials with 

 which it works, how it gets these materials, how it changes them, and what 

 the final products are. 



8. How does the character of the soil affect the degree to which plants 

 may take up the soil water ? 



9. Assuming that your school ground is the bottom of a water tank, 

 the side and end walls of which are as high as required for the following 

 problem, how high would the column of water be which is given off in the 



