FLOWERS AND THEIR WORK 



37 



after coming together, unite to form a single cell. This process 

 is known as fertilization. This single cell formed by the union 

 of the pollen tube cell or sperm and the egg cell is now called 

 a fertilized egg. 



Development of Ovule into Seed. The 

 primary reason for the existence of a flower 

 is that it may produce seeds from which future 

 plants will grow. The first beginning of the 

 growth of the seed takes place at the mo- 

 ment of fertilization. From that time on 

 there is a growth within the ovule of a lit- 

 tle structure called the embryo. The embryo 



will give rise to the future plant. After ferti- I 1 i 



lization the ovule grows into a seed. 



Problem VII. A study of cross-pollina- 

 tion and some rtieans of bringing it about. 

 (Laboratory Manual, Prob. VII.) 



(a) Adaptations in the flower. 



(&) Adaptations in an insect agent. 



(c) Other agents. 



History of the Discoveries regarding Pol- 

 lination of Flowers. Although the ancient 

 Greek and Roman naturalists had some 

 vague ideas on the subject of fertilization, 

 it was not until the latter part of the eight- 

 eenth century that it was demonstrated that 

 pollen was necessary for the growth of the 

 embryo within a seed. In the latter part 

 of the eighteenth century a book appeared 

 in which a German named Conrad Sprengel 

 worked out the facts that the structure of 



, . n . , Fertilization of the 



certain flowers seemed to be adapted to O vule. A pistil cut 

 the visits of insects. Certain facilities were 

 offered to an insect in the way of easy 



. ,, , , . ,, . , . 



foothold, sweet odor, and especially food in 

 the shape of pollen and nectar, the latter 



down lengthwise (only 

 one * de shown >- The 



pollen tube is seen en- 



tering the cavity (lo _ 

 cule) of the ovary. 



