MODIFICATIONS 



137 



stems which grow upon or under the soil. They are divided 

 into nodes and internodes: From the nodes grow leaves, 

 stems and roots; types of rhizomes, rhizomes that grow erect 

 are vertical, those that grow parallel to the soil are horizontal, 

 those that grow at an oblique angle are oblique; nature of 

 rhizome, rhizomes are simple when they do not branch, but 

 branched when lateral .buds develop into branches. 



FIG. 78. Modified Stems. 1, Tear-thumb (Polygonum arifolium) with 

 small hook-shaped prickles; 2, wild smilax (Smilax rotundifolia) with large 

 prickles; 3, asparagus (Asparagus officinalis) with leaf -like divisions of the 

 stem; 4, wild grape (Vitis cestivaUs) with stem modified as tendril; 5, haw- 

 thorn (Cratcegus coccined) with a stem modified as a thorn; 6, Virginia 

 creeper (Parthenocis.sus quinquefolia) with a stem modified as a tendril with 

 enlarged discs. 



2. Bulbs. Bulbs are fleshy storage stems and are classified 

 as scaly, tunicated, solid and compound. The scaly bulb, as 

 that of the lily, is made up of numerous separate fleshy 



