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 ■viith 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.^ 



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 potar 

 toes to try to find a branching specimen. If such a one is secured, 

 sketch it. 



I Examination of a lot of potatoes will usually discover specimens with an 

 inch or more of attached stem. 



