268 



STRUCTURE OF STEMS AND ROOTS 



wood and bast, and also the amount of fundament al 

 tissue. Use the highest power and draw a portion includ- 

 ing one strand of wood and two of bast. In this por- 

 tion draw the tissues from the center out beyond the 

 endodermis. Sections may also be made of the roots of 

 germinating pumpkins or squashes. 



Review. — Name two types of stems found among flowenug 

 plants. Describe each and give examples to illustrate them. Give 

 the plan of arrangement of bundles in fern stems. How many types 

 of bundles are there? Upon what do their differences depend? 

 Describe and give examples of collateral bundles. What difference 

 is there betwpen open and closed collateral bundles? Give examples 

 of each. . Describe and give examples of concentric bundles. Radial 

 arrangement. What is secondary thickening ? What plants show it ? 

 What is the layer called which forms the new cells in a bundle? 

 When is this layer most active? Describe the work of this layer. 

 What part of each bundle of a dicotyledon is found in the bark? 

 What are lenticels? What is phellogen? Describe the work of phel- 

 logen in any plant you have studied. Where is the root cap? 

 What is its use? Describe fully the structure of roots, telling how 

 they differ from stems. 



Note to Paragraph 422. — In woody stems tiie compression is 

 such that the student is usually puzzled to understand the bundle 

 structure. The subject will be simplified if he compares (on cross- 

 section), the bundles in such a plant as the cucumber with that 

 part of the vascular ring which lies between any two medullary 

 rays in one-year old stems of peach, elm, oak, etc. 



All material and apparatus should be kept under cover when not in 



