170 STEMS 
which supply the plant during the dry season. In the stems of 
Sorghum and Sugar Cane, so much sugar is accumulated and re- 
tained that these plants are grown for the sugar which they afford. 
In the stems of trees much food is stored in the form of starch, 
and when transferred to grow- 
ing regions during early spring, 
it is changed to sugar, in which 
form it occurs in solution in 
the sap of the tree. The so- 
called maple sap obtained from 
the Sugar Maple is a good illus- 
tration of sap which contains 
much stored food in the form 
of sugar. In early spring be- 
fore the leaves appear, the trees 
are so gorged with sap that it 
can be drawn off by boring into 
the wood and inserting spiles. 
This sugar comes from reserve 
food accumulated when the 
leaves are active, and serves as 
Fic. 147. — A branch of Myrsiphyl- 9 supply for the growth of new 
aeons pie ie foliage at the beginning of the 
growing season. . 
Some stems, notably those of the Irish Potato, contain large 
amounts of starch on account of which they are valuable for food. 
Another tuber-like stem similar to that of the Irish Potato is pro- 
duced by the Jerusalem Artichoke —a plant of the Sunflower 
type and often grown on account of the food value of its under- 
ground tubers. 
Many of the early spring plants, such as Spring Beauty, Dutch- 
man’s Breeches, Wind Flower, some Violets, and many other 
plants having a supply of food at hand can spring up quickly, 
flower, and accumulate another supply of food before the sunlight 
is excluded by the forest foliage. Such plants, being seen only 
in April or early May, have what is called the vernal habit, i.e , 
they live their life cycle in the spring of the year. The food 
reserve of stems has much to do with the vernal habit. 
Classes of Stems. — There are many ways in which stems may 
be classified. Stems are classified as monocotyledonous or dicoty- 
