28 NATURE TEACHING 



of roots arise from the stem, at some distance above the 

 soil, grow downwards and anchor the plant firmly. In 

 the screw-pine such roots are still more obvious, and 

 form curious, stilt-like supporting structures. The ivy 

 furnishes another excellent example of adventitious roots 

 borne on the stem. In this case they are of assistance 

 to the plant, supporting it when climbing up trees, walls, 

 etc. 



In the case of many plants, a portion of the stem, 

 separated from the parent plant, so that it no longer 

 receives supplies of water and food, shows a tendency to 

 attempt to save its life by producing roots of its own. 

 In this effort it will usually be successful if it happens to 

 be placed in a moist position. A piece of watercress 

 placed in a bottle of water quickly develops a number of 

 adventitious roots. Full advantage is taken of this 

 tendency by gardeners and agriculturists. Many orna- 

 mental plants are propagated in this way. Pieces of the 

 stem are cut ofT and placed in moist earth, when new 

 roots soon make their appearance, usually from near the 

 cut end of the stem, and a new plant is obtained. Roses, 

 geraniums, chrysanthemums, and a number of other 

 .garden plants are regularly propagated in this manner. 

 .In tropical countries this method of propagation is used 

 for many important food crops, for example, sugar-cane, 

 sweet potato, and cassava (the source of tapioca). 



Nor is it only from stems that roots may be developed. 

 Some leaves, when plucked from their parent plant and 

 laic! on moist soil, will throw out roots and leaf-buds, so 

 that, in a little time, a number of young plants may be 

 raised from a single leaf. The leaves of" fibrous-rooted " 



