CHAPIER VIII. 



GROWTH AND MOVEMENT. 



Artists style vegetable objects collectively " Still Life." But to the 

 physiologist these words are contradictory, for he knows that Movement 

 of some sort or another is the most notable evidence of active Life. In 

 the Living Plant movements may be of various sorts : (i) Molecular, 

 which cannot be seen except by the results, these becoming apparent 

 as chemical change ; (ii) Movements of the Protoplast : these are visible 

 under the microscope, but not with the naked eye, and as they are 

 confined within the cell-wall they do not alter the form or position 

 of the cell as a whole ; (iii) Movements of the shoot or root as a whole, 

 or of its parts. These last movements are the most obvious, but as they 

 are usually slow, time is necessary for their observation. They may 

 be referred to changes in the constituent cells. One reason for their 

 slowness is no doubt the fact that the protoplast of each cell, though 

 it is the vital agent, is not so free to move as are the protoplasts of the 

 animal body : for it is encysted by its cell-wall. Like the mediaeval 

 knight its movements are checked by its protective armour. The 

 Plant has sacrificed mobility for mechanical defence. Though move- 

 ment is occasionally present in mature parts, it is in young and still 

 growing parts that it is habitually seen. There is indeed a close 

 relation between growth of the plant-body, or of its parts, and Move- 

 ment. It will then be well first to enquire into the nature of Growth 

 and the conditions which determine it, before passing on to the study 

 of Movement. 



Growth. 



The most obvious sign of Growth is increase in size. But as applied 

 to a living organism the term connotes something more intimate 

 than mere enlargement. It has been seen in germination (p. 5) 

 that growth involves transfer and change of materials, which cannot 



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