ROOTS 101 



called positive heliotropism ; the opposite is known as nega- 

 tive heliotropism. 



Suggestion. To show negative heliotropism of roots 

 plant seedlings on cloth over water in a tumbler or battery 

 jar. Cover the outside of the jar with black paper so as to 

 exclude light from the roots. Make a slit or small hole 

 through the cover paper so as to admit light at one point. 

 Keep the apparatus standing in the same position for sev- 

 eral days. (See Figure 40.) 



Remove the cover and note the position of the root. 



If the experiment has been carefully prepared, the root 

 tip will be found pointing away from the aperture where 

 light entered. 



Suggestion. Test carrots, parsnips, beets, radishes, 

 turnips, etc., for starch, cane and grape sugar, and protein. 

 Which are richest in starch? in sugar? Why do we eat 

 radishes raw, while potatoes must be cooked ? 



Separate some of the cortex from the central cylinder 

 of several roots and test each tissue separately for the va- 

 rious nutrients. From the results of such tests what do 

 you conclude is the principal place of food storage in roots ? 

 Is there any relation between the size of a root and its food 

 contents ? 



Reference Work. Find out how beet sugar is obtained, 

 tracing the process from seed time to the manufactured 

 product. 



95. ROOTS 



Object. To learn the effect of nutrient solutions upon 

 the growth of young plants. 



Directions. Select two young cabbage plants about 

 three or four inches tall and place them in two bottles, 



