THE STEM 93 



them in coloring fluid for four or five hours, then divide into 

 cross and vertical sections, as shown in Figs. 107, 108, and 

 draw, labeling the parts that you can make out. Through 

 which has the liquid ascended most rapidly? Test with 

 iodine and find out in which part nourishment is most abun- 

 dant. It is this abundant store of food that makes the 

 potato such a valuable crop in cold countries like Norway 

 and Iceland, where the seasons are too short to admit of the 

 slow process of developing the plant from the seed. 



Compare a common potato with a sweet potato. Are 

 there any eyes or buds on the latter ? Is there a scale below 

 them? Do they occur in any regular order? Do you see 

 any lenticels? The common potato and the sweet potato 

 are both tubers ; can you give some of the reasons why the 

 one is regarded as a modi- 

 fied branch, and the other 

 as a root? (100.) Com- 

 pare their food contents; 

 which contains most 

 starch? Which most 

 sugar? How can you 

 judge about the sugarwith- Fig. i09.-scaiy Fig no. - Scaiy 



•■ * , . , , To bud of oak, enlarged. bulb of lily (Gray). 



out a chemical test ( 



107. The bulb is a form of underground stem reduced to a 

 single bud. Get the scaly bulb of a lily, and sketch it from 

 the outside and in cross and vertical section. Compare it 

 with the scaly winter buds of the oak and hickory, or other 

 common deciduous tree. Make an enlarged sketch of the 

 latter on the same scale as the lily bulb, and the resemblance 

 will at once become ai:)parent. The scales of the bulb are, in 

 fact, only thick, fleshy leaves closely packed around a short 

 axis that has become dilated into a flat disk. From the center 

 of the disk, which is the terminal node of this transformed 

 stem, rises the flower stalk, or scape, as it is called, of the 

 season. After blossoming, the scape perishes with its bulb, 

 and their place is taken by new ones which are developed 



