232 STRUCTURE AND VITAL PROCESSES OF PLANTS 



3. THE STEM 



The work of the stem can be said to be threef61d. It has 



1. to support the branches and leaves, and to spread them 

 out to the air and the sun; 



2. to carry the sap from the roots up to all parts of the 

 plant, and to bring the elaborate food, formed in the green parts 

 of the plant, down to the points where growth takes place; 



3. to serve as a food-store for use of the plant in the future. 



A- Stems as Means to spread out the Leaves and 

 Flowers to the Air and the Sun. 



We have learned that the inner cells of leaves are workshops 

 wherein the plant prepares materials for the construction of its 

 body. As this can only be done under the influence of sunlight, 

 and also as carbon can only be taken from the air, it follows 

 that the leaves must be freely spread out to the sunlight and to 

 the air. The same is necessary for the flowers also in order 

 that they may be pollinated by the agency of insects or the wind 

 so as to produce fruit. Stems, therefore, rise up, and, in many 

 cases, form branches on which they support a great number of 

 leaves and flowers. 



1. Growth and Description of Stems. 



The topmost end of the stem consists of very tender cells 

 which, by division, multiply at a quick rate. Stems, therefore, 

 grow there in length, and we call these points points of groivth. 

 As the stem grows, leaves are developed on its sides. The places 

 where the leaves rise are often swollen and are, therefore, denoted 

 nodes, the parts between the nodes being called hdernodes. The 

 internodes are of ditterent lengths in difl'erent plants: they are 

 generally long in grasses, l)ut slioit in plants forming leaf-rosettes 

 (see Elephantopus, p. 206). 



The internode may be flliform r^ thread-like (Horse Gram); or 

 succulent = fleshy (Balsam); or nodose = swollen at the nodes 

 (Adliatoda); or tuberose — swollen like a tuber (Knolkohl); or 



