CHAPTER XXVI 

 GENERAL CHARACTERISTICS OF GROWTH 



Consider the lilies of the field, how they grow. 



— Matthew 6:26. 



What Is Growth? — In the previous chapters, those aspects of 

 the life of the plant which deal with nutrition have been studied. 

 The phases of activity concerned with catabolism and anabolism 

 have been the focus of attention. We now turn to the question of 

 growth, which, in fact, cannot be separated from these previous 

 questions except as a pedagogical convenience. The term growth 

 involves two distinct ideas which are not always carefulfy dis- 

 tinguished. First, growth means an increase in size, and, to some 

 writers, this is all that there is in it. Gager states that "the im- 

 mediate cause of all growth is osmotic pressure," which indicates 

 that he has in mind this purely mechanical increase in size, which 

 is brought about largely by the intake or absorption of water. 

 Thus a flaccid cell placed in water may be said to grow. A dry 

 board which imbibes water is also growing, and this purely me- 

 chanical growth may be imitated or reproduced in artificial cells. 



It is true that cells will not grow unless they are in a state of 

 turgidity, but other observers have modified this purely mechan- 

 ical definition of growth by including in it the conception of the 

 formation of new parts or organs. As a plant grows, new tissues 

 and organs are formed, and it is this formation and differentiation 

 of parts which is the main feature in growth, according to the sup- 

 porters of this view. In many plants the roots contract during 

 development, pulling the plant more firmly into the ground. 

 Oxalis roots may shorten 4-6 cm. In the dandelion (Taraxacum) 

 this shortening takes place at the top of the root (morphologically 

 the " stem-root," where these two organs merge into each other 

 in this so-called "stemless" plant) and may equal 20% of the 

 entire length of the "root." Those who emphasize the differ- 

 entiative and formative phases of growth, consequently, consider 

 that these roots are growing even though they are shortening. 



The champions of growth as mere increase in size prefer to 



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