NATURE OF PLANTS 



III 



tivated land. Plowing and hoeing only serves to break up the 

 rhizome into numerous parts each of which may develop buds 

 and roots from their nodes and so establish new plants. 



49. The Condensed Type of Stems. — In many cases we find 

 that the food is localized in special regions of the rhizome which 

 consequently become enlarged and rather fleshy, such enlarge- 

 ments appearing at the end of the rhizome or scattered along its 

 entire length. Such modified parts of a rhizome are called tubers, 

 e. g., the potato and Jerusalem artichoke (Fig. 72). The potato 



Fig. 71. Fig. 72. 



Fig. 71. Rhizome of Solomon's seal with aerial shoot just emerging from 

 the ground. The seal-like scars mark the successive shoots produced during 

 the past three years. 



Fig. 72. Formation of tubers: A, old potato or tuber with two shoots 

 reaching up into the air and from the base of these shoots, rhizomes have been 

 formed that are developing new tubers. B, mature tuber with spirally ar- 

 ranged buds, the so-called "eyes" of the potato, 



is formed by the storage of foods in certain parts of the rather 

 small rhizomes that branch out from the stem of the plant. 

 The "eyes" are the buds that develop at each node of the rhizome 

 and each is capable of forming a shoot, although but a few of 

 them so function, as is the case in an ordinary branch of a tree. 

 By passing a thread around a potato so that it touches each 

 successive bud you will see that there is the same arrangement of 

 the buds as appears in the leafy stem. There is considerable 

 evidence to show that the tuber form of rhizome originated 

 through association with fungi. Thus in the potato the rhizomes 

 appear to have a vigorous normal growth through the soil until 



