CHAPTER II. 



GROWTH. 



I. Elongation of dicotyledonous stems The body 



of a plant con tinues to in<;req pe in <;i>p mn je or le ss coat inu- 

 ouslY.duiing__its._entiieJife. As a consequence, bulk is largely 

 determ ined by ag e, although in many forms the death and ex- 

 cision of certain parts of the body take place at such rate that 

 but little net gain is shown. The^ra te of increas e and the vari- 

 ations in Jhe rate are illustrated by the following experiments : 



Select a vigorous young specimen of bean {^Phaseolus), bind- 

 weed [Polygonuni), or sunflower {Helianthus) in a greenhouse, 

 or, under suitable conditions, in the open air. If the plant is 

 in a pot or box, lay it on its side on a table, support the stem 

 by means of a number of thicknesses of board, and place a 

 ruler with its edge against the stem. If the plant cannot be 

 adjusted in this manner, arrange a clamp and support to hold 

 a ruler against the stem, and parallel to it, in an upright position. 

 Bend a small piece of steel wire 12 centimeters long into the 

 form of a V, and tie a silk thread to the ends of the arms in 

 such manner that it will be kept taut by the spreading of the 

 arms. Moisten the thread with India ink, using a quill or splint 

 of wood to apply the fluid to it. Place the ruler so that it 

 covers a section 25 cm. in length, beginning at the tip. Now 

 press the thread on the stem, opposite the centimeter divi- 

 sions of the ruler, making a single clear, sharp line. Place 

 the plant in its customary position, and under normal condi- 

 tions. Measure the intervals between the inked lines a day 

 later, and repeat on the third and fourth days. The total 



