66 



Principles of Plant Culture. 



minutes or longer, to exhaust it of free oxygen, and then 

 cool it quickly by setting the dish containing it in cold 

 water. Now place a healthy cutting (358) of some 

 plant that roots freely in water, as willow, nasturtium or 

 wandering jew,* in each of two tumblers. Pour a part 

 of the cool, boiled water into one of the tumblers and 

 add a little olive oil to for.m a film over the liquid thus 

 preventing it from absorbing more air. Then agitate 

 the rest of the water vigorously to impregnate it again 

 with oxygen, and pour some of this into the second tum- 

 bler. Set both tumblers in a light, warm place. In a 

 few days roots will start freely from the slip in the tum- 

 bler in which the 

 water has access to 

 the air, but not in the 

 other (Fig. 27). If 

 now the rooted cut- 

 ting is placed in oil- 

 covered water that 

 has been exhausted of 

 its oxygen by boiling, 

 the roots will soon die. 

 The copious forma- 

 tion of root-hairs 

 (101) that reach out 

 into the moist atmos- 

 phere of t h e s e e d- 

 tester (39), and that 

 so often fills the soil 



FIG. 27. Slips of Tradescantia in water con- cavities with a deli- 

 taining oxygen (left glass) and in water con- 

 taining no oxygen (right glass). From nature. Cate, COttOliy dOWU, IS- 



* Tradescantia. 



