UNDERGROUND STEMS 



37 



bear roots at regular intervals and show well-defined leaf scars 

 at the nodes. Some grasses, such as the witch grass, have 

 similar underground stems bearing buds at the nodes. When 

 such grass stems are torn to pieces by the farm implements each 



FIG. 29. Potato showing the tuber type of stem. Fia. 30. Stem or trunk of the 



birch showing the peculiar markings 

 of the bark. 



bud is capable of growing into a new plant. Such stems are 

 called root stocks or rhizomes. Shortened stems have very short 

 internodes and are generally designated as bulbs (Fig. 28) and 

 tubers (Fig. 29). The bulbs are very short stems covered with 

 scales which are really modified leaves. These scales may be 



