EXERCISE 77 

 WHAT ARE ROOT HAIRS? 



Materials. Drinking-glasses; filter paper; seeds of radish, mustard, or oats. 



Directions. Cut a strip of filter paper 4 inches wide and 2 inches longer than the circumfer- 

 ence of the glass at its top. Fold the paper lengthwise with each fold 2 inches wide. Turn 

 and crease one fold again, thus making a short fold each side of which is 

 1 inch in width. With a needle or pin perforate the crease of the short fold 

 in many places, and place seeds in this fold. Place the filter paper with the 

 wide fold innermost around the upper inner wall of the drink ing-glass, allow- 

 ing the ends to fit together. Pour water into the glass until the lower part of 

 the wide fold is wet. The water will then cause the filter paper to adhere to 

 the glass and will moisten the seeds. Observe from day to day, and as they 

 develop describe the roots and root hairs with reference to general appearance, 

 length, diameter of hairs, location of hairs on roots, and abundance of hairs. 



Additional problems. If a microscope is available, mount some of the root hairs, together with the root, 

 from which they grow, and make a detailed study, showing the exact relation which exists between the 

 root hairs and the surface cells of the root. Determine where the young root hairs are developing. How 

 do they grow ? Can you estimate the proportionate surface exposure of root hairs as compared with that 

 of the roots from which they grow ? 



Plant seeds such as those used above in dishes of moist sawdust or sand ; when the young plants 

 have developed until a good supply of root hairs are formed, carefully pull up some of the plants. To 

 'what parts of the root system is most soil attached ? What holds the soil ? What is meant by " anchorage 

 in the soil " ? 



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