METABOLISM— DIGESTION— TRANSLOCATION— GROWTH 2 15 



have penetrated the soil and its leaves have spread out into the 

 air. It is also seen in bulbs, tubers, fleshy stems, roots and 

 leaves, in vi^hieh the stored food feeds new plants or is used ip the 

 producing of flowers, fruits and other organs. 



Phases of Growth. — There are vejy naturally three phases 

 of growth: (1) the 'origin and formative phase, (2) the enlarge- 

 ment and elongation phase and (3) the maturing phase. 



The origin and foiinative phase involves cell divisions, the 

 formation of new tissues and the production of new organs. It 

 is especially prominent in the growth of the seedling, in the 

 g^wth of shoots and leaves in the spring and usually in the 

 formation of flowers and fruits. The enlargement phase in- 

 volves the enlargement of cells and organs, and varies in different 

 parts of the plant and at different seasons of the year. We have 

 already learned that there is a zone of elongation in the root tip 

 (see page 67) and in the tips of growing shoots (see page 46) ; 

 and that the thickening of the dicotyledonous stems and roots is 

 due to the growth and cell division in the cambium (see page 

 48). The enlargement of buds, shoots, leaves, flowers and 

 fruits at certain seasons of the year is very evident to the most 

 casual observer. The maturing phase involves cell-wall thick- 

 enings and many complex physiological and chemical changes. 

 The maturing of buds is very necessary in order to prepare the 

 plant for the winter season of our temperate zone. The maturing 

 and ripening of fruits and seeds is a phenomenon with which 

 we are all familiar, but which involves chemical processes which 

 we do not thoroughly understand. 



In general, it may be said that the ripening of -fruits involves 

 the breaking down of the cell walls and the changing of starches 

 into sugars as a result of the action of the enzymes. These 



