PROBLEM 2. The Fart Stems and Roots Flay in Making Food 



growth began. It was made by the last year's termi- 

 nal bud. Do this with several twigs of the same spe- 

 cies. Are all the distances the same? What would 

 you have to do before you could draw general con- 

 clusions from your measurements? 



10. How does a stem grow in thickness? Copy 

 Fissure 187, a longitudinal section through the pith 

 and wood of a five-year-old sapling. The bark is 

 not shown. At the bottom of your copy put the 

 numbers i to 5 using i to represent the wood pres- 

 ent when the tree started its existence. Five repre- 

 sents the most recently formed wood. Draw a cross 

 section at each of the levels a, b, c, and d. Where 

 ought you to cut the section to determine the full 

 age of a tree? What is the general shape of the 

 trunk? Why? 



11. {a) Why should you not twist a wire tightly 

 around a young tree? {b) When you remove the 

 bark from a t:\\ig why does the wood lying just 

 underneath feel wet and slippery? {c) How can a 

 botanist by studying a cross section of a very old 

 tree know that the year 1750 in that particular re- 

 gion was a dry year and the year 1820 was a wet 

 one? 



12. How does a monocotyledonous stem differ 

 from a dicotryledonous stem? Cross and longitudinal 

 sections of young cornstalks make good material 

 for the study of vascular bundles in a monocot stem. 

 How many bundles are there in your cornstalk? 

 Where are they? How do they feel? Describe the 

 covering of the stem. 



13. How does the narrowness of a tube affect the 

 rise of water through it? Place hairlike glass tubes of 

 varying thickness into colored water. What differ- 

 ences do you note? Make accurate measurements 

 and record. With a magnifying glass examine the 

 top of the column in the widest tube. What do you notice? Explain. 



14. Does water leave a plant? Use a vigorously growing potted plant. 

 Insert one of its branches into a large test tube (one inch diameter). Plug 

 the open end with cotton and suspend the tube in a clamp on a ring 

 stand. Water the plant and place in the light. What do you observe after 

 half an hour and again after several hours? Are you ready to draw con- 

 clusions? What else should you do? 



15. How much water is lost by an actively transpiring plant? Water 

 a plant. Enclose the plant pot and the soil in a rubber sheet so that 



163 



Fig. 187 Diagram of 

 a longitudinal section 

 through a ^-year-old 

 woody stem. (See Ex- 

 ercise 10) 



