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 

 /* 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- B 1 i 



lization the ovule grows into a seed. 



Problem VII. A study of cross-pollina- 

 tion and some means of bringing it about. 

 (Laboratory Manual, Prob. VII.) 



(a) Adaptations in tlie flower. 



(#) Adaptations in an insect agent. 



(r) 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 

 certain flowers seemed to be adapted to 

 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 



Fertilization of the 

 ovule. A pistil cut 

 down lengthwise (only 

 one side shown). The 

 pollen tube is seen en- 

 tering the cavity (lo- 

 cule) of the ovary. 



