STUDIES OF SEED-PLANTS 



183 



(L) Examine a tuber of potato, or artichoke. Note the point 

 where it was attached to the main stem of the plant. Examine the 

 "eyes," which are buds. Each "eye" is capable of developing a new 

 plant, and hence to avoid having too many plants in one place 

 gardeners cut tubers into pieces, each having two or three "eyes." 

 Dig up a potato plant, and note position of the old and the new 

 potatoes. 



Bulbs are short and greatly enlarged underground stems, 

 producing stalks and leaves from the upper surface and roots 

 from the lower. The onion is a good example of a bulb. A 

 longitudinal cut through the center shows it to be a short 

 stem surrounded by the 

 thickened layers, which are 

 modified leaves. Indian tur- 

 nip (Jack-in-the-pulpit) and 

 crocus have similar short 

 and bulb-like stems, but 

 they are solid and not com- 

 posed of layers like the 

 onion. Such solid short un- 

 derground stems are often 

 called corms; but there is 

 no sharp distinction and 

 corms are often called solid 

 bulbs. 



"Stemless" Plants. 

 Many common plants (e.g., 

 dandelions, plantains) have short stems and are often in- 

 correctly said to be " stemless." 



177. Condensed Stems above Ground. Tubers and 

 bulbs have been mentioned as examples of condensed under- 

 ground stems. The various forms of cacti are condensed 

 stems above ground. The flattened leaf-like parts of prickly- 

 pear cactus are not leaves, but branches of the stem. The 

 thorns are reduced leaves. The flat and thickened branches 

 not only perform the ordinary work of leaves, but are also 



FIG. 54. Potato plant, developed from 

 dark-colored tuber in center. New 

 tubers are thickenings of underground 

 branches of the stem. (From Stras- 

 burger.) 



