CHAPTER III. 



GROWTH OF ROOTS, STEMS, AND LEAVES. 



Do all parts of the root continue growing as it pushes down 

 into the soil ? 



Ex. 3. To answer this we must have the roots where we can examine 

 them. Germinating bean or pumpkin seeds may be placed upon moist 

 cotton wool and held in place by strips of sheet 

 cork fastened together by rubber bands. Suspend 

 in an inverted flower pot over a saucer of water. 

 When the roots have grown about an inch and 

 a half, mark off equal distances on them with 

 ink (waterproof ink is better). Place the ger- 

 minator under cover, and observe the next day. 

 The spaces toward the upper end nearest the 

 seed will be the same distance apart they were 

 the day before. The root has not grown there 

 nor at the tip. Growth in length is greatest just 

 at the back of the tip. 



In a similar way examine the growth 

 of stem and leaves. Mark off equal dis- 

 tances as before ; they may be a little 

 farther apart on the stem. The place on 

 a stem from which leaves are given off is 

 called a node. The part between two 

 nodes is called an internode. Notice 

 that the stem grows both below and above 

 each internode, but the greatest elonga- 

 tion is in the upper half of an internode. How does a leaf 

 become larger? 



Now compare the results with the growth of monocoty- 

 ledons. 



x8 



F I G. 25. — Seedlings 

 marked to show the 

 place of greatest 

 growth. 



