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 m 
judge about thesugarwith- Pie Say fe U0 Ss 
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 apparent. 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 
x es 
