HOW STEMS ELONGATE 



17 



season). The Irish potato is a stem: the 

 sweet potato is probably a root. 



46. HOW STEMS ELONGATE.— Eoo^s elongate 

 by growing near the tip. Stems elongate by 

 growing more or less throughout the young 

 or soft part or "between joints." But any 

 part of the stem soon reaches a limit beyond 

 which it cannot grow, or becomes "fixed;" 

 and the new parts beyond 

 elongate until they, too, 

 become rigid. When a part 

 of the stem once becomes 

 fixed or hard, it never in- 

 creases in length: that is, 

 the trunk or woody parts 

 never groiv longer or higher; 

 branches do not become far- 

 ther apart or higher from 

 the ground. 



47. The different re- 

 gions of growth in stems 

 and roots may be observed in seedling- 

 plants. Place seeds of radish or cabbage 

 between layers of blotting-paper or thick cloth. Keep 

 them damp and warm. When stem and root have grown 

 an inch and a half long each, with waterproof ink 

 mark spaces exactly one -quarter inch apart. Keep the 

 plantlets moist for a day or two, and it will be found that 

 on the stem some or all of the marks are more than one- 

 quarter inch apart ; 

 on the root the marks 

 have not separated. 

 The root has grown ^.i 

 beyond the last mark . 

 Figs. 25 and 26. 



. 01(1 mullein 

 stalk, with 

 strict habit of 

 growth. 



21. Exeurreut trunk. 

 A pine. 



