CHAPTER X 
GROWTH 
116. Definition. Growth is increase in size of either the 
organism as a whole or of any of its parts. By growth the 
individual protoplast of a cell may become more bulky, 
the chloroplasts or leucoplasts may become larger, the 
nucleus bigger, the cell-walls thicker, the cell as a whole 
may increase in any dimension, and, as a result of this, 
the tissues and organs, and finally the entire organism, 
may become larger. Growth does not always involve the 
whole organism. Cell- walls often grow thicker while the 
size of the plant as a whole does not alter. Growth often 
involves a decrease in the size of one or more of the parts ; 
thus, when a potato "sprouts," the tuber itself, giving its 
substance to nourish the newly formed stems, becomes 
smaller and lighter in weight, while the stems increase in 
size and weight. As a whole, however, the potato plant 
is growing (Fig. 60). 
116. Osmotic Pressure and Growth. Growth does 
not always involve increase in weight. If, for example, 
the osmotic pressure increases within a turgid cell, and if 
the cell- walls are elastic, the cell will grow bigger in one or 
more dimensions. Not only may this growth involve no 
increase in weight (as, for example, when the increase in 
osmotic pressure within a cell is due merely to the chang- 
ing of starch to sugar), but may even be accompanied by 
loss of weight on account of waste products being given 
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