106 EXPERIMENTAL PLANT PHYSIOLOGY 



this experiment. A sunflower or 



broad - bean seedling answers well. 



The upper part of the stem, for a 



distance of about ten centimetres from 



the apex, is marked off by transverse 



lines mto lengths of five millimetres 



each. The marks can be made with 



Indian ink by means of a small 



camel's-hair brush. 



Fig. 56 (a) is a drawing on a re- 

 duced scale of a broad- 

 bean seedling, the actual 

 length of whose stem 

 at the beginning of the 

 experiment was about 

 twenty-five centimetres. 

 A length of ten centi- 

 metres from the tip was 

 marked off into five 

 millimetre divisions. 

 Fig. 56 (b) shows the 

 lengths of the measured 

 portion of the stem on 

 the first, second, sixth, 

 and tenth days, the scale 

 to which the figure is 

 drawn being three-quar- 

 ters of the actual lengths 

 measured. 

 Observations. — In the case of the 



broad-bean seedling observed it was 



found : 



1. That growth in length took place 

 through a distance of about 4'5 centi- 

 metres from the apex. 



2. That all the growing part does "o 

 not elongate at the same rate ; the ^ ^ 

 region of maximum growth changes 2 2 

 its position from day to day, keepmg ii «o 

 at a distance of about 1'5 centimetres 

 from the apex. 



(Fig. 56 a) 







Fin. 56 (6) 



