114 FOUNDATIONS OF BOTANY 
Cut thin cross-sections of twigs of some common deciduous tree 
or shrub, in its early winter condition, moisten with iodine solution, 
and examine for starch with a moderately high power of the micro- 
scope. Sketch the section with a pencil, coloring the starchy por- 
tions with blue ink, used with a mapping pen, and describe exactly 
in what portions the starch is deposited. 
122. Storage in Underground Stems. — The branches 
and trunk of a tree furnish the most convenient place 
in which to deposit food during winter to begin the 
growth of the following spring. But in those plants 
which die down to the ground at the beginning of winter 
the storage must be either in the roots, as has been 
described in Sect. 58, or in underground portions of 
the stem. 
Rootstocks, tubers, and bulbs seem to have been de- 
veloped by plants to answer as storehouses through the 
winter (or in some countries through the dry season) for 
the reserve materials which the plant has accumulated 
during the growing season. The commonest tuber is the 
potato, and this fact and the points of interest which it 
represents make it especially desirable to use for a study 
of the underground stem in a form most highly specialized 
for the storage of starch and other valuable products. 
123. A Typical Tuber: the Potato. — Sketch the general outline 
of a potato, showing the attachment to the stem from which it grew.1 
Note the distribution of the “eyes,” — are they opposite or alter- 
nate? Examine them closely with the magnifying glass and then with 
the lowest power of the microscope. What do they appear to be? 
If the potato is a stem, it may branch, — look over a lot of pota- 
toes to try to find a branching specimen. If such a one is secured, 
sketch it. 
1 Examination of a jot of potatoes will usually discover specimens with an 
inch or more of attached stem. 
