VEGETATIVE OEGANS OF PLANTS. 275 



vial, inserting a sprig of the common greenhouse-plant 

 Tradescantia zebrina, so that the cut end of the stem 

 shall stand in the water, and finally corking the vial air- 

 tight. The plant, which is very tenacious of life, and 

 usually grows well in spite of all neglect, is not checked 

 in its vegetative development by the treatment just de- 

 scribed, but immediately begins to adapt itself to its 

 new circumstances. In a few days, if the temperature 

 be 70 or thereabout, air-roots will be seen to issue from 

 the joints of the stem. These are fringed with a profu- 

 sion of delicate hairs, and rapidly extend to a length of 

 from one to two inches. The lower ones, if they chance 



Fig. 41 



to penetrate the water, become discolored and decay ; the 

 others, however, remain for a long time fresh, and of a 

 white color. 



Some plants have roots which are equally able to exist 

 and perform their functions, whether in the soil or sub- 



