THE STEM 



91 



FIO. 104. Root- 



nature becomes apparent only after a careful examination. 

 But while the chief function of underground stems is the 

 storage of nourishment, they serve other purposes also. In 

 plants requiring a great deal of moisture, 

 like the ferns, and in others growing in dry 

 places and needing to husband moisture 

 carefully, like the blackberry lily, under- 

 ground stems may be useful in preventing 

 the too rapid evaporation that would take 

 place through aerial stems. Defense against 

 frost, cold, heat, and other dangers, as well 

 as quickness of propagation, are also attained 

 or assisted by this means. 



105. Rootstocks and rhizomes. From a 

 prostrate stem like that shown in Fig. 95 to a 



creeping rootstock like the one in Fig. 104, the stock of creeping 

 transition is so easy that we find no difficulty panic grass ' 

 in accounting for it. From the prostrate rootstock to the 

 thickened storage rhizome (Fig. 105) of such plants as the iris, 

 puccoon, bulrush, and Solomon's-seal, is a longer step, but 

 the bud with its leaf scales at the growing tip, a, the remains 

 of the flower stem at the node, 6, and the roots from the under 



surface sufficiently indicate its na- 

 ture. The peculiar scars from which 

 0- the Solomon's seal takes its name 

 are caused by the falling away 

 each year of the flowering stem 

 a, growing bud at of the season after its work is done, 



the tip ; b, remains of the past i 11*1.11 i e j.i 



season's flower stem; c ,c,c, scars leaving behind the node of the un- 

 of old stems. (After GRAY.) derground stem from which it orig- 

 inated. In this way the rhizome lives on indefinitely, 

 growing and increasing at one end as fast as it dies at 

 the other. Test a little of the substance of the rhizome 

 with iodine. Of what does it consist? Of what use is it 

 to the plant? 



1 06. The tuber. A still further thickening and shorten- 



c c 



