CHAPTER V 

 ADAPTATIONS OF THE NUTRITIVE ORGANS OF PLANTS 



54. The nutritive organs of plants. From our study of 

 food manufacture (29-34) we learned that the plant foods are 

 produced in green leaves. Before this process of food manu- 

 facture can go on, however, the cells in the leaf must be sup- 

 plied with raw materials from the air and from the soil. 

 Since the roots, stems, and leaves are all concerned in food 

 making, these organs are known as the nutritive organs of 

 plants. Each of these organs has several functions ; we shall 

 now learn what some of these functions are, and how the 

 nutritive organs are adapted for the work they do. 



I. THE STRUCTURE AND ADAPTATIONS OF ROOTS 



55. The structure of roots. Laboratory Study No. 29. 

 A. Gross structure of roots. 



Select the largest roots of a well-developed seedling or the 

 roots of common weeds. By means of your thumb and finger 

 nail gently scrape off the outer layers from a piece of one of 

 these roots. When no more of the material can be easily 

 removed by this method, pick to pieces the central part of 

 the root which is left. The outer layer you have removed is 

 largely composed of the cells of the cortex, and the central 

 part that has been exposed is called the central cylinder. 



1. Tell what you have done. 



2. Which is composed of the tougher and harder material, 



the cortex or the central cylinder ? 

 39 



