SOME LESSONS IN BOTANY 59 
THE STEM 
This term not only refers here to the main stem of the 
plant, but also includes all of its branches down to the 
smallest twigs. We have seen that the important work 
of the plant is done by the 
leaves and the roots. The prin- 
cipal use of the ordinary stem, 
therefore, is to serve as a means 
of communication between these 
two organs, and to support the 
leaves and distribute them in 
such a manner as to expose 
them to air and sunlight to the 
best advantage. 
The shape and habit of stems 
vary so greatly that it is well 
to notice some of the more in- 
teresting forms. A few of the |” 
chief types are shown in the ac- 
companying figures. 
Type 1. In this type the 
main stem runs straight upward 
to the top of the tree. All the 
branches are much smaller. The 
head of the tree has a conical 
and symmetrical form. Ex- Eim 
amples: spruce, pine, and balsam. 
Type 2. In this type the trunk divides into several large 
branches, and there is no straight, central stem extending 
to the top. This usually gives the head a broad or rounded 
form. Examples: box elder, elm. 
