68 PRACTICAL COURSE IN BOTANY 



regularity to answer the purpose. Tie a piece of thin cloth over the mouth 

 of each bottle and invert with the necks extending an inch or two into 

 empty tum!)lers placed beneath. Fill all to the same height with soils of 

 different kinds — sand, clay, gravel, loam, vegetable mold, etc. — and pour 



Fig. 82. — Apparatus for testing the capacity of soils to take in and retain 

 moisture. 



over each the same quantity of water from above. Watch the rate at 

 which the liquid filters through into the tumblers. Which loses its mois- 

 ture soonest ? Which retains it longest ? 



Next leave the soils in the bottles dry, fill the tumblers up to the necks 

 of the bottles, and watch the rate at which the water rises in the different 

 ones. The power of soils to absorb moisture is called capillarity. Which 

 of your samples shows the highest capillarity ? Which the lowest ? Do 

 you observe any relation between the capillarity of a soil and its power of 

 retention ? 



68. Roots as holdfasts. — One use of ordinary roots is 

 to serve as props and stays for anchoring plants to the soil. 

 Tall herbs and shrubs, and vegetation generally that is 

 exposed to much stress of weather, are apt to have large, 

 strong roots. Even plants of the same species will develop 

 systems of very different strength according as they grow 

 in sheltered or exposed places. 



