248 GROWTH 



to left or in a direction the opposite to that of the hands 

 of a clock; but the apex of the stem of a hop, honeysuckle 

 and some other plants moves round from left to right when 

 nutating. 



By means of such movements roots are enabled to make 

 easier progress through the soil, and climbing stems and ten- 

 drils which nutate very conspicuously are enabled by the same 

 means to reach neighbouring supports around which they wind. 



The ends of the subterranean shoots of many dicotyledonous 

 plants are bent round by the excessive growth of one side 

 in the manner indicated in Figs. 4, 144. By such arrangement 

 the delicate tissues of the terminal buds are considerably 

 protected against injury when the shoot is growing forward 

 or upward through the soil. After such a bent shoot emerges 

 from the soil, rapid growth takes place on its concave side and 

 the curved portion soon becomes straight. 



In a young state the leaves forming the buds of plants are 

 curved round the delicate growing-point or curled up in a 

 characteristic manner in consequence of the growth of one side 

 of each leaf proceeding faster than that of the other side : when 

 the buds open the side which previously grew more slowly grows 

 at a greater pace and the curled leaf consequently unfolds and 

 eventually becomes flat. 



In most stems the pith and cortex continue to grow for a 

 longer period than the woody tissue : the pith and cortex strive 

 to elongate but the woody tissue hinders them to a certain 

 extent. The result of such unequal growth is the production 

 of longitudinal tensions in the growing parts. On splitting in 

 two the stems of elder, sunflower and other rapidly growing 

 plants longitudinally the pith elongates a little and the two 

 separated halves curve outwards. 



The bark of many trees does not grow so rapidly as the wood 

 within, and consequently becomes more or less stretched. 



It must be mentioned that movements of plant organs and 



