74 PHYSIOLOGICAL PROCESSES IN PLANTS 



Conclusion. What influence do you think the force of 

 gravity has on roots ? 



2. EFFECT OF MOISTURE 



Observation. Plant soaked mustard or radish seeds on the 

 outer side of a moist sponge and suspend it under a bell jar 

 where there is plenty of light and moderate temperature. 

 Observe results. 



Conclusions. 1. What effect does moisture have on grow- 

 ing roots ? 



2. W'hich influence seems to be the more powerful, mois- 

 ture or gravity ? 



b. Structure 



1. BOOT HAIRS 



Method. Sow radish seeds on moist earth in a pan, or next to the 

 glass sides of a funnel, so that as the rootlets develop, they may be seen. 

 Or, put a cutting, as tradescantia, in a bottle of water, and note the fine 

 fuzzy growths on the rootlets. 



Observations. 1. Find fuzzy, hairlike whitish structures on the root- 

 lets. They are called root hairs. Where are they the longest ? Where 

 the most abundant ? 



2. Examine them with the low power of a microscope. Are their 

 walls thick or thin ? 



Conclusions. 1. Tell fully just what you think is the pur- 

 pose (function) of root hairs. 



2. Why should root hairs be thin ? 



Note. Root hairs increase the absorbing surface of roots from 50 to 

 100 times. 



2. FLESHY ROOTS 



Method. Cut a cross section through a fleshy root as a car- 

 rot or parsnip (taproot) and dip in iodine. Also cut a length- 

 wise section, and stain. 



Observations. 1. What part is stained the most, the outer 

 part (cortex) or the inner part (central or woody cylinder) ? 



2. Find some small whitish branches or cores of wood run- 



