# fbr ELEMENTS OF BOTANY. 
to starch. When they are depositing starch in any part of 
the root or stem for future use, the withdrawal of sugar from 
those portions of the sap which contain it most abundantly 
gives rise to a slow movement of dissolved particles of 
sugar in the direction of the region where starch is being 
laid up. 
96. Storage of Food in the Stem. —'The reason why the 
plant may profit by laying up a food supply somewhere inside 
its tissues has already been suggested, § 70. 
The most remarkable instance of storage of food in the 
stem is probably that of sago-palms, which contain an 
enormous amount, sometimes as much as 800 pounds, of 
starchy material in a single trunk. But the commoner plants 
of temperate regions furnish plenty of examples of deposits’ 
of food in the stem. As in the case of seeds and roots, starch 
constitutes one of the most important kinds of this reserve 
material of the stem, and since it is easier to detect than any 
other substance which the plant employs for this purpose, the 
student will do well to spend the time which he devotes to 
the study of storage of food in the stem to looking for starch 
only. 
Cut thin cross-sections of twigs of any common hard-wood tree, in its 
winter condition, moisten with iodine solution, and examine for starch 
with a moderately high power of the microscope. Sketch the section, 
and describe exactly in what portions the starch is deposited. 
97. Storage in Underground Stens.— The branches and 
trunk of a tree furnish the most convenient place in which to 
deposit nourishment 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 § 46, or in underground 
portions of the stem. 
Rootstocks, tubers, and bulbs seem to have been developed 
by plants to answer as storehouses through the winter (or in 
