CHAPTER VI. 



GROWTH. 



52. Nature of Growth. — The increase of the living substance 

 of an organism is designated growth, and it is generally accom- 

 panied by an increase in weight and size. This increase does 

 not, however, always accompany growth; indeed, it was de- 

 monstrated in Experiment 29 that a plant may grow while 

 losing in weight. If the plant is accumulating storage material 

 it will, on the other hand, undergo an increase in weight not in 

 any manner connected with growth. It is also to be noted 

 that independent changes in form and size occur which are due 

 simply to alterations in the force of turgor and in the extensi- 

 bility of the cell-walls. Lastly, growth does not consist in the 

 formation of new cells ; on the contrary, the formation of new 

 cells is a result of growth. 



EXPERIMENT 86. 



MEASUREMENT OF GROWTH EXTENSION. 



To determine the increase in length of a plant the simple auxa- 

 nometer shown in Fig. 64 will be found fairly accurate. This appa- 

 ratus consists of an upright stand 50 cm. in height to which is 

 attached a horizontal arm 10 era. in length. To the end of this 

 arm is attached a wooden pulley 4 cm. in diameter, in such manner 

 that it will turn freely. To one side of this pulley is fixed a thin 

 wooden pointer 20 cm. in length. This pointer is made from a 

 strip not more than 2 mm. in thickness, and has wrapped around 

 the larger end at ^ a sufficient quantity of tinfoil to balance the 

 longer end. A curved paper-scale ruled to 2 mm. is held by 

 another stand near the tip of the pointer. A linen or silk thread 



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