CHAPTER II. 



GROWTH. 



i. Elongation of dicotyledonous stems The body 

 of a plant continues to increase in size more or less continu- 

 ously during its entire life. As a consequence, bulk is largely 

 determined by age, 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 rate of increase and the vari- 

 ations in the rate are illustrated by the following experiments : 



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

 weed (Polygonum), or sunflower (Htlianthus) 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 1 2 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 



