Storage Stems and Leaves. 



49 



EXERCISE 29. 



\Read and discuss in the class, ,] 



Storage Stems and Leaves. 



Perennial herbs have persistent under- 

 ground stems from which aerial stems, 

 or at least leaves and flowers, grow 

 every year. These stems may usually 

 be distinguished from roots by buds or 

 by rudimentary leaves. They all con- 

 tain more or less starch, particularly at 

 the close of the growing season. Those 



which 



Fig. 32. Horizontal rootstocks of smilacina (false 

 Solomon's Seal) and Oregon oxalis. a. Bud for the 

 next growth of leafy stem. b. The scar left by the 

 above-ground stem of last year, c and d. Similar 

 scars of preceding years, e and/. Dormant buds. 



Fig. 31. Vertical rootstock 

 of calla. 



are rootlike, or 

 somewhat woody, or not 

 much distended with 

 stored food are usually 

 called rootstocks * (See 

 Figs. 31 and 32). In the 

 last exercise we learned 

 that stems like potatoes, 

 and those shown in Fig. 

 33, are called tubers. 



Tubers, unlike most 

 fleshy rootstocks, are a 

 means of multiplying the 



* Our most troublesome weeds such as field morning-glory, known in 

 England as bindweed, prostrate heliotrope, or blueweed, and licorice, common 

 on rich bottom land, are not easily exterminated because their numerous long and 

 slender rootstocks are not injured but benefited by ordinary cultivation which 

 makes cuttings of them and thus multiplies and spreads the plants. 



