NATURE OF PLANTS 105 



very difficult to eradicate plants of this type. This is very well 

 illustrated in the quack grass, often a troublesome pest in cul- 

 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 modified 

 parts of a rhizome are called tubers, e. g., the potato and Jerusa- 

 lem artichoke (Fig. 72). The potato is formed by the storage of 



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. 



foods in certain parts of the rather small rhizomes that branch out 

 from the stem of the plant. The "eyes" are the buds that de- 

 velop 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. 



A great variety of plants develop only very short stems that 

 are more or less buried in the ground. This type of stem modi- 



