THE GROWTH OF BOOTS AND STEMS. 189 



one only. Scrape the root of Carrot and that of Parsnip, put the 

 scrapings in warm water, shake up, and filter. Test the filtrate for 

 sugar with Fehling's solution. The reserve food in the Beet is also 

 sugar, but it is cane-sugar, not glucose, as in Carrot, etc. Hence, in 

 order to get the red precipitate with Fehling's solution, it is necessary 

 to boil first with sulphuric acid in order to convert the cane-sugar to 

 glucose. 



(c) Examine the tuberous roots of Dahlia, which are formed in 

 summer and store up food to be used by the flowering stems of the 

 next year (Fig. 62). When exhausted of food they die off, but new 

 tubers are formed as the old ones are emptied, so that the individual 

 plants can carry on a perennial existence. The reserve food in this 

 case is inulin, similar in composition to starch, but differing in being 

 soluble in water, so that in a section of fresh root examined in water 

 the cells appear empty. If a piece, or a section, of Dahlia tuber be 

 placed in alcohol for some time, the inulin is deposited in the cells as 

 rounded crystal-like masses. 



QUESTIONS ON CHAPTER VII. 



1. Explain how you would investigate the rate of growth in length 

 of a root, indicating the precautions you would observe in conducting 

 your experiments. Illustrate your answer by a diagram. 



2. Describe simple experiments to show by what paths water travels 

 through the plant from roots to leaves. 



3. What are the main functions of roots ? How are they adapted to 

 carry on these functions ? 



4. How is the radicle of a seedling enabled to penetrate stiff soil ? 

 How may the force exerted by the radicle be measured ? 



5. How can it be proved that the direction of growth of a root 

 is a response to the stimulus of gravity ? Explain the term " geo- 

 tropism." 



6. How is the direction of growth of a root affected by moisture ? 

 Why is it advantageous to the plant that the stimulus due to moisture 

 is able to overcome that due to gravity ? 



7. Describe the structure of the stem in any Monocotyledon, as seen 

 in longitudinal and in transverse sections. 



8. In what features of structure and function do the vessels of the 

 phloem (sieve-tubes) differ from those of the wood ? 



9. What is the vascular bundle ? Of what parts does a vascular 

 bundle in the stem of a Dicotyledon consist, and what are their 

 respective functions ? 



