116 STEMS 



Where are these bundles largest? Where smallest? 

 Where are they closest together ? What advantage is there 

 in this arrangement ? Draw one bundle magnified. 



Note. It will be remembered that the corn seed embryo had 

 only one cotyledon. Such a seed is called monocotyledonous, a 

 word which means having one cotyledon. All plants which spring 

 from monocotyledonous seeds are very much alike in the character 

 of their stems, leaves, and flowers. Such plants are known as 

 monocotyledons, or briefly monocotyls. Plants which produce seeds 

 of two or more cotyledons are dicotyl plants. 



109. STRUCTURE 



Object. (a) To learn the gross structure of a, woody 

 (dicotyl} stem. 



(&) To learn the fine structure of a woody stem. 



Apparatus. Twigs of woody plants one and two years old, also 

 a few sections of stems several years old in which the rings are easily 

 seen. Horse-chestnut, ash, and ailanthus are excellent for the 

 former; and oak, hard pine, ash, and chestnut are good for the latter. 



(a) Method. Follow the same general plan as in the pre- 

 ceding Experiment, making out as many answers to the fol- 

 lowing as possible: By what is the stem covered? What 

 scars and markings are to be seen? What is the cause or 

 meaning of each such scar or mark? Are the joints or 

 nodes conspicuous? Describe the buds and their covering 

 and protection. Where is the pith ? How much ? Its color 

 and other peculiarities if any? The wood? Its arrange- 

 ment? How may you tell the age of a stem? Find the 

 rays or lines which extend from the central pith outward 

 toward the bark. 



How many layers of bark are distinguishable? How 

 many annual rings? In an old stem find the heartwood 

 and sapwood. 



