Plants in Relation to Man 521 



presence and relative abundance. You have already found it in the 



potato. Prepare in the same way and apply the starch test to such 



food plants as the carrot, turnip, onion, and others available. ' Corn, 



wheat, barley, rice, and other grains may readily 



be examined in this way. Cut a grain of wheat 



transversely (Fig. 159), scrape very delicately a 



little of the endosperm and spread it out in a 



little water on a microscope slide. Cover with 



a thin glass and examine with a low-power 



microscope. Put a drop of iodine solution at the ^ 



edge of the cover glass and note its effect upon 



the particles. Does the color produced indicate p IG . 159. _ Length- 



the presence of starch? Stems, last year's buds, wise section of the 



and roots may be examined. Cut exceedingly wheat g ra f n - Flour is 



thin cross sections, immerse them for a moment " ' 



in iodine solution, and then mount in water on a 



microscope slide. Examine closely and observe in what parts of the 



tissue the largest amount of starch is indicated. 



SUMMARY 



Plants manufacture their own food ; differing in this from animals. 



The materials used are soil water and carbon dioxid from the air. 



Sugar is manufactured in the chloroplasts of the green leaves by 

 the aid of the energy of sunlight. The process is called photosyn- 

 thesis. The sugar may be converted into starch in the leaf. The 

 presence of starch is shown by the iodine test. 



Plants manufacture proteins also, which contain nitrogen and some- 

 times sulfur and phosphorus. 



Proteins are abundant in seeds. 



Starch is insoluble. It is changed in the leaf into soluble sugar 

 by a digestive ferment, or enzyme, known as diastase. 



The sugar produced in the leaf is carried in the sap to various parts 

 of the plant and may remain as sugar or be converted into cellulose 

 and other substances, from which new growth is made or new plants 

 started. 



Plants store up food either for their new growth or for their off- 

 spring, in various centers, such as seeds, fruits, buds, stems, roots 

 and root stalks, bulbs, and tubers. Many of such stores are appro- 

 priated for food by man and other animals. 



