THE FLOWER 237 



water. Gardeners know, for instance, that rain during 

 the flowering period interferes with fertihsation. Under 

 these conditions the flowers remain sterile and produce 

 no fruit. In order that the fertilisation of Vallisneria 

 may take place in the air the plant is provided with 

 the following ingenious adaptation. The female 

 flowers (left-hand side) grow almost at the bottom of 

 the water, on very long but tightly coiled stalks. When 

 the flowering season approaches these stalks uncoil 

 and grow, thus bringing the female flowers up to the 

 surface of the water. By this time the male flowers 

 which develop similarly at the bottom of the water 

 (right-hand side) are torn from their stalks and 

 also rise to the surface of the water. Floating among 

 the female flowers they open their anthers and shed 

 their pollen, some of which falls on the stigmas of 

 the female flowers. When the flowering period is 

 over, the stalk of the female flower coils up again, 

 carrying the fertilised flower down to the bottom of 

 the water, where the further development of the fruit 

 takes place. 



The significance in a plant's life of the pollen and the 

 ovule — the essential parts of the flower — is now quite 

 clear. The adaptations described above which make for 

 their mutual interaction are also comprehensible. But 

 another question springs up : what is the significance of 

 the remaining parts of the flower ? What is the pur- 

 pose of the calyx ? What is the use of the carpel 

 which only hinders the access of pollen to the ovules ? 

 Why have the petals such bright colours and some- 

 times such fantastic shapes ? What is the purpose of 

 the perfume of flowers, and, finally, of the sweet honey- 

 like fluid secreted at the bottom of the corolla by the 

 well-known clover, dead-nettle, and many other flowers ? 

 Let us try to answer these questions. The significance 

 of the calyx and the carpel is the most intelligible of 

 them all. The former, like the external scales of leaf- 



