How Plants Draw in Various Materials 197 



different positions or directions in the soil, the former seeking 

 usually the dampest places, while the latter tend rather to pene- 

 trate radiately from the stem into the earth. 



While absorption and anchorage are the typical functions of 

 roots, occasionally they perform others quite different, as we 

 have noticed already in the chapter on leaves and stems. Thus, 

 they become modified, with appropriate anatomical changes, to 

 swollen storage organs, in the Sweet Potato; to slender and 

 toughened climbing organs in English Ivy and many tropical 

 climbers; to tough pointed spines in some Palms; to slender 

 penetrating haustoria or sucking organs in some parasites; to 

 flat green photosynthetic organs in some tropical orchids; and to 

 yet other structures of minor account. Thus roots, like stems 

 and leaves, formed for one function can be modified greatly for 

 the performance of others, illustrating once more Nature's won- 

 derful capacity for ringing changes on her favorite ideas. 



