FLOWERS AND THEIR WORK 



37 



after coming together, luiHe 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 Ovuje jnto Seed, — iThe j 

 primarp^jceascmr-fof"the existence of a flower r 

 is that it may produce seeds from which futur^ 

 plants will grouKl 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 

 iL'ill give rise to the future plant. After ferti- 

 lizgition the ovule grows into a seed. 



Problem VII. ,J study of a-oss-pnllinw- 

 tion and some means of iringin^ it about. 

 (Laboratory Manual, Frdb. VII.) 



(a.) , Idaptations in the flower. 



(b) Adaptations in an insect agent. 



id) Other agents. , 



History of the Discoveries regarding Pol- 

 lination of Flowers. — Although the ancient 

 Greek and Ex)man naturalists had some 

 vague ideas on the subject of fertilization, 

 it was not imtil 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 ca- 

 tering the cavity (lo- 

 cule) of the ovary. 



