GERMINATION, GROWTH, TISSUE TENSION. 151 



rapidity is reached, after which it gradually diminishes until growth 

 ceases altogether. This rise and fall in the growth rate, extending 

 over the whole of a growth period, is called the "grand period of 

 growth." 



196. Grand Period in Boots. Some additional simple 

 experiments 011 the grand period of growth should be made. 

 Place a germinating Bean or Pea in the bulb of a long 

 thistle-tube, so that the root can grow down the tube. 

 Set the tube in a bottle containing water ; put wet sphagnum 

 or cotton-wool in the bulb with the seed. Read off the 

 length of the root daily with a scale ; or gum a strip of 

 paper along the tube, each day at the same hour mark the 

 position reached by the root-tip and measure the intervals 

 (the daily amounts of growth). 



197. Grand Period in Shoots. Grow Phaseolus 

 seedlings in pots of soil, and make daily measurements 

 of the epicotyl (the stem region between the cotyledons 

 and the paired primary foliage-leaves) ; as long as the 

 tip of the epicotyl remains curved, measure with a strip 

 of paper. 



Also measure separately the daily growth in length of 

 the successive internodes of a Bean or Pea seedling, and 

 note that (1) each internode shows a grand period; (2) 

 when the internodes have fully elongated the oldest are 

 usually relatively short, then come longer ones (the fifth, 

 counting upwards, is generally the longest in the Pea), 

 while the youngest internodes are again shorter this is 

 another example of the grand period. 



Since these results are obtained with plants kept in 

 darkness and at constant temperature, we may infer that 

 the growth energy of the different internodes varies owing 

 to internal causes. 



198. Distribution of Growth in Growing Organs. The 



preceding experiment suggests a simple method for finding out 

 whether or not any portion of a growing organ elongates uniformly, 

 i.e. for investigating the distribution of rate of growth in 

 length of roots, stems, etc. All we have to do is to mark the 

 organ with parallel transverse lines at regular short intervals, 



