CHAPTER XIV

STEMS

WHAT ARE STEMS FOR?

Visit the farm or garden and the fields to examine stems and study their general appearances and habits of growth.  Notice that many plants, like the trees, bushes and many vegetable and flowering plants, have stems which are very much branched, while others have apparently single stems with but few or no branches.  Examine these stems carefully and note that there are leaves on some part of all of them and that just above the point where each leaf is fastened to the stem there is a bud which may sometime produce a new branch (Fig. 68).  If the stems of trees and other woody plants be examined in the winter after the leaves have fallen, it will be seen that the buds are still there, and that just below each bud is a mark or leaf scar left by the fallen leaf.  These buds are the beginnings of new branches for another year’s growth.  On some branches will be found also flowers and fruit or seed vessels.

Buds and leaves or buds and leaf scars distinguish stems from roots.  Some plants have stems under the soil as well as above it.  These underground stems resemble roots but can be distinguished from them by the rings or joints where will be found buds and small scale-like leaves (Fig. 69).  Quitch-grass or wiregrass, Burmuda grass, white potato and artichoke are examples of underground stems.

Now study the habit of growth of these stems.  Notice that: 

Some plants grow erect with strong, stiff stems, for example, corn, sunflower, maple, pine, elm and other trees.  Many of these erect stems have branches reaching out into the air in all directions.  Stand under a tree close to the stem or trunk and look up into the tree and notice that the leaves are near the outer ends of the branches while in the centre of the tree the branches are nearly bare.  Why is this?  If you remember the work of leaves and the conditions necessary for their work you will be able to answer this question.  Leaves need light and air for their work, and these erect, branching stems hold the leaves up and spread them out in the light and air.

Notice that where several trees grow close together, they are one-sided, and that the longest and largest branches are on the outside of the group and that they have more leaves than the inner branches.  Why?  Why do the trees in thick woods have most of the living branches and bear most of their leaves away up in the top of the tree?

Some stems instead of standing up erect climb up on other plants or objects by means of springlike tendrils which twist about the object and so hold up the slender stem.  On the grape vine these tendrils are slender branches.  On the sweet pea and garden pea they are parts of the leaves.  The trumpet creeper and English ivy climb by means of air roots.  The nasturtium climbs by means of its leaf stems.