STEMS, BULBS AND BUDS 55 



of the socalled " birdVeye wood." Otheirs may lie dormant 

 for many years and then be stimulated into activity. 



The Growth of the Monocotyledonous Stem. — The growth 

 of this type of stem also involves (1) cell division, (2) cell en- 

 largement and (3) cell differentiation into tissues. However, 

 the position of the meristem or cambium and its behavior are 

 quite different. From the arrangement of the bundles it will be 

 readily seen that there can be no cambium ring (Fig. 23). The 

 cambium is active only at the tips of the bundles and for a short 

 time in that part of the bundle just above the node. The increase 

 in diameter of the steiu is due primarily to the enlargement of the 

 cells of the permanent tissues. Of course, such a stem cannot 

 increase in diameter indefinitely as in the case of the dicotyle- 

 donous stem. There are some few exceptions to this which we 

 will not discuss at this time. The fibro-vascular bundle of the 

 Indian com (Fig. 23), which may be takem. as a type of the 

 monocot stem ; the central part is composed of tracheary tissue, 

 with a mass of sieve tissue on the side nearest the surface of the 

 stem, all of which is surrounded by fibrous tissue. 



Functions of Stems. — The primary functions of the stems 

 are the support of the foliage, flowers and fruits in the air and 

 sunshine and the transportation of food materials and foods 

 from one part of the plant to another. We will learn a little later 

 (Chapter V) that the foliage has a very definite relationship to 

 the air for the exchange of atmospheric gases and to the sunlight 

 from which it obtains its energy for work. Therefore, the char- 

 acter of the stem must be such as to bring about these relation- 

 ships. We will also learn (Chapter IV) that the plant obtains 

 its water and many food materials from the soil. Therefore, 

 there must be some system for the transfer of food materials and 



