26 BOOTS 



a germinator, and also on plants that have been grown in loose 

 soils. They grow between the very fine particles of soil. If 

 the plant is pulled from hard soil they are torn off, but if 

 pulled from loose, wet soil, they are retained and the soil clings 

 to them. In order to understand them it will be necessary to 

 study them with a microscope. 



FIG. 16. Seedling showing FIG. 17. Cross-section of rootlet showing root-hairs, 

 soil held by root-hairs. 



Work of Root-Hairs. Each root-hair is a thin-walled cell 

 containing living protoplasm and cell sap. This living proto- 

 plasm has the power of absorbing water by osmosis, causing the 

 cells to become very much expanded or turgid. The excess of 

 certain substances in the soil may cause an exosmosis or with- 

 drawal of water from the roots and thus injure or even kill the 

 plant. This explains one reason why certain soils may be 



