304 GROWTH 



388. Correlative Changes in Growth Due to Injuries. It is well 

 known that the destruction of one of the branches of a shoot is 

 followed by the accelerated development of other contiguous 

 branches for the purpose of taking up the functions of the lost 

 member. It may also be demonstrated by the following experi- 

 ment that an injury to an organ of the shoot is followed by re- 

 sponses in the most distant parts of the body. 



Germinate a number of seedlings of Pisum or Phaseolus until 

 the roots are about 2 cm. in length. Select a dozen of equal 

 development and make a thin mark with India ink near the base 

 of the root, and measure the distance exactly to the tips, keeping 

 the records identified with every specimen. Fix the seedlings in 

 small cylinders filled with water, by means of perforated cork 

 stoppers, allowing the roots to be submerged. Remove the 

 shoots from half of the plants by .means of a sharp knife, cutting 

 cleanly across immediately above the cotyledons. Set all of the 

 preparations in a moist chamber consisting of a large bell-jar at a 

 temperature of 20-22 C. Measure the lengths of the roots 24, 

 48, 72, and 1 20 hours later. Ascertain the difference in the 

 amount of growth shown by the roots of the normal and decapi- 

 tated plants. Follow the growth of the plants for a week and 

 find what length of time is necessary to equalize the rate of 

 elongation of the roots and shoots in both series. 



Repeat the experiment, but cut away the roots instead of the 

 shoots and note rate of growth of the shoots in the normal and 

 mutilated specimens. Special precautions must be taken to pre- 

 vent desiccation of the latter by the use of cotton wool moistened 

 with water. 1 



389. Movements Due to Correlations in Growth. The general 

 position of every organ relative to the main axis, and to other 

 branches is assumed in response to correlative changes in growth. 

 Such positions are not identical in all stages of development. In 



1 Townsend, C. O. The correlation of growth under the influence of injuries. 

 Annals of Botany. 11:509. 1897. 



See also, Hering, F. Ueber Wachstumscorrelation in Folge mechanischer Hem- 

 mung des Wachsens. Jahrb. Wiss. Bot. 29 : 132. 1896. 



