CHAPTER III. 



GROWTH. 



Growth and extension, Growth of cells. Growing points. Growth of 

 roots, stems, and leaves. Form as dependent on growth. Move- 

 ments dependent on growth. Movements of protoplasm. Tur- 

 gescence. Circurnnutation of roots, stems, leaves. Seedling plants. 



IN considering the growth of plants we have to distin- 

 guish that growth which is mere extension of old material 

 from that which is the result of the formation of new 

 substance. We have an illustration of the first case in the 

 earliest stages of germination of a seed, or in the sprouting 

 of a potato in a cellar. Growth may and does take place 

 in such instances without any real increase of substance, or 

 any augmented weight save what may be derived from water. 

 The plant in this stage lives upon the resources stored up 

 in its tissues, and will continue to do so till they are 

 exhausted. But growth, in the sense of real increase of 

 substance or of increased weight from the addition of new 

 material, depends upon the amount of carbon assimilated, 

 as already referred to under the heading of leaves. A plant 

 with leaf-green or chlorophyll in its tissues (and it is with 

 these alone that we are here concerned) gains carbon in the 

 form of carbonic acid gas when it is exposed to light, and 

 loses it constantly, whether in light or darkness. Never- 

 theless, as the total gain is greater than the loss, the 

 balance is in favour of the plant. The plant may thus be 



