STEMS 109 



tip divide and push forward, leaving dead cells 

 behind them. 



147. Growth in length and diameter. — Dead cells 

 do not increase in size, of course, so that the trunk 

 of a tree does not elongate except at the tips of 

 the stems and branches. Thus a branch on the 

 trunk will always remain the same distance from 

 the roots. Its distance from the ground might be 

 increased by the washing away of the soil below it. 

 This may be demonstrated if a nail is driven in 

 the trunk of a tree near the surface of the soil, 

 and a second as high above it as may be conven- 

 ient. Measure the distance between them quite 

 exactly, and then repeat a few months or a year 

 later. 



148. Measurement of growth in length. — Mark 

 the stem of some rapidly growing plant, such as 

 bean or sunflower, with India-ink at intervals of 

 half an inch. Measure these intervals on three or 

 more successive days. Do all of them increase ? 

 What part of the stem increases in length with 

 greatest rapidity? 



149. Measurement of groivth in diameter. — The 

 increase in diameter of a plant is not so easily 



