144 



GREEN PLANTS AS POOD MAKERS 



developed greatly thickened walls, which give mechanical support 

 to the tubelike cells. Collections of such tubes and supporting 

 woody cells together make up what are known as fibrovascular 



bundles in the wood. By this 



Central Cylinder- 

 i§s£\._>*6oc{y bundle 



-root "hour 



epicCermis 



..root 



cctp 



system of tubes water is sent 

 quickly from the roots to all 

 parts of the plant body, pre- 

 venting withering of leaves, 

 and enabling the leaf to use 

 water in food manufacture. 



Practical Exercise 3. What would 

 you say was the use to the plant of 

 a carrot root? Of the aerial roots 

 of an ivy plant ? 



How would you go to work to 

 find out what food substances are 

 stored in a turnip or radish root? 

 Of what value would these sub- 

 stances be to the plant ? 



Laboratory Exercise. What 

 are root hairs and where are 

 they found ? 



Grow radish or mustard seeds 



;;|||lpl on blue blotting paper in Syra- 



"%S'-' J - cuse wa ^ch glasses, covering 



v '^Zr^ each watch glass with a thin 



A root, highly magnified. Find and give the glass plate. Describe the strUC- 

 functions of the root cap, the woody bundles, and tures you see growing from the 



theroothairs - roots. These are called root 



hairs. Where are they the longest? Where the most abundant? 



Place root hairs of radish or mustard on a glass slide. Mount in a 

 drop of water and cover with a cover slip. Examine with the low 

 power of a microscope. What can you say of the thickness of their 

 walls? Of how many cells does a root hair consist? If the root were 

 covered with these thin-walled, delicate structures, what effect would 

 they have upon the amount of absorbing surface of the root? 



Root hairs. Root hairs vaiy in length according to their position 

 on the root, the longest root hairs being found some distance back 

 from the tip. They are outgrowths of the outer layer of the root, 

 the epidermis, and are of very great importance to the living plant. 



A single root hair examined under a compound microscope 

 will be found to be a long, threadlike structure, almost color- 

 less in appearance. The cell wall, which is very flexible and thin, 



