44 NATURE TEACHING 



that we do not find green leaves in every case, as in 

 underground stems the leaves are more commonly 

 reduced to dry, scale-like bodies. 



The iris or flag, and Solomon's seal afford good 

 examples of stems of this kind, running horizontally in 

 the ground, bearing scale leaves, leaf-buds, and roots. 

 Stems of this nature are usually spoken of as rJiizomes. 

 Those leaf-buds which grow above the surface of the 

 soil form green leaves, but the underground portion of 

 the stem bears nothing but dry scales. 



A potato is an enlarged and swollen stem, and not a 

 root. Leaves are almost absent, being represented only 

 by the " eyes? which are in reality leaf-buds, as is easily 

 seen by keeping some potatoes in a damp place for a 

 time, when the " eyes " will grow, developing finally into 

 well-marked stems bearing leaves. Stems of the nature 

 of the potato are known as tubers. The Jerusalem 

 artichoke is interesting, as its underground stem, with 

 its very well-marked scale leaves, serves to connect up 

 the type of stem met with in the iris and Solomon's seal, 

 and true tubers, such as the underground potato stems. 



Rhizomes and tubers are examples of stems which 

 are adapted to a special purpose, namely, to hold stores 

 of food for the future use of the plant. 



In the iris the underground stem keeps on growing, 

 year after year, and by its branching serves also to pro- 

 pagate the plant, for, as the older portions die away, the 

 branches become separated and form independent plants. 

 In the potato this is still more marked, each potato plant 

 forming each year a large number of tubers, every one 

 of which can the next year form one or more new potato 



