CHAPTER V 



UNDERGROUND STEMS ; STORAGE IN STEMS AND LEAVES ; 

 REPRODUCTION 



64. Characteristics of underground stems. The popular notion 

 of what a stem is, includes the idea that it is an aerial part of 

 the plant. It is easier to recognize as roots such structures 

 as the aerial roots of corn and of poison ivy than it is to rec- 

 ognize as stems the thickened underground portions of iris, 

 jack-in-the-pulpit, dragon-root, trillium, or potato. Frequently, 



like aerial stems, underground 

 stems are divided into nodes 

 and internodes ; and many of 

 them bear scales which repre- 

 sent leaves, and produce buds 

 in the axils of these scales. 

 Such buds are well shown in 

 the underground stems of some grasses. 

 Dicotyledonous underground stems usu- 

 ally have distinct bark, wood, and pith, 

 while most dicotyledonous roots do not 

 have pith, though some do. 



FIG. 59. A May-apple plant, showing the history of the rootstock 



1 is the oldest surviving portion of the rootstock ; 2 is a year younger ; 3 a year 

 younger than 2, and so on. At each figure the cluster of roots marks the position 

 of the base of the upright stem for that year, as is shown at 6. b, bud for the new 

 year's growth; br, bract at the base of the present stem. One sixth natural size 



72 



