Chapter 5. 



FLOWERS AND THEIR FORMATION. 



Conditions favouring the production of flowers. Structure and 

 functions of the various parts of a flower. Pollination and 

 Fertilisation. Self -fertile and self-sterile flowers. Ripening of 

 fruits and seeds. 



In speaking- of the difference between vegetative and 

 reproductive organs, in the first chapter I have already 

 mentioned that certain external conditions which favour 

 the development of the former affect adversely the forma- 

 tion of flowers. Long horticultural practice has also 

 proved that the developineni of floral organs can be 

 stimulated in various ways which are well known to 

 gardeners. Thus reduction m the supply of water and 

 consequent stoppage of the luxuriant development of 

 leaves is one of the chief methods employed. It has been 

 found by scientific experiments that these various horti- 

 cultural practices are based upon definite physiological 

 requiremients. In recent years much has been done to 

 confirm and extend our knowledge of this subject. It 

 was proved that bright illumination of plants is essential 

 for the production of flowers. At first it was thought 

 that certain rays of light influenced the development in 

 the plant of special flower-forming substances, and early 

 experiments seemed to indicate that these were produced 

 by definite rays of light from beyond the blue end of the 

 spectrum — rays of light w^hich are known to have great 

 chemical activity. More recently, however, it seems to 



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