278 



REPRODUCTION OF HIGHER PLANTS 



In the process of fertilization in a flower a 

 sperm nucleus unites with an egg cell nucleus 

 to form the embryo of the future plant. The 

 other sperm nucleus unites with a pair of 

 nuclei, the polar nuclei. This latter union re- 

 sults in the endosperm nucleus which divides 

 and, in time, forms the food supply for the 

 embryo. Double fertilization is characteristic 

 of flowering plants. 



the process of fertilization. The 

 union of the sperm and egg nu- 

 clei forms the one-celled embryo 

 which develops into a tiny 

 plant. The union of the other 

 sperm nucleus and the polar 

 nuclei forms the cell that starts 

 the endosperm which is the food 

 supply of the tiny plant. This 

 double fertilization results in the 

 future plant and its food supply. 

 Formation of the seed and 

 fruit. There are ducts going 

 from the plant through the 



..remains of stigma 

 ccnol 



placenta of the ovary to the ovule. 

 Food passes through these ducts, 

 which nourishes and effects the 

 rapid division or cleavage of cells 

 in the tiny embryo in the ovule. 

 At the same time, the endosperm 

 tissue of the ovule grows rapidly and 

 stores the future food supply for the 

 embryo. As the embryo develops 

 into a many-celled structure, dif- 

 ferentiation of the cells sets in and 



the first root or kypOCOtyl, the first 

 bud Or plumule, and the Seed leaves 



Or Cotyledons are formed. Ihe en- 

 - . , . 



dosperm develops at the same time. 



~~3>lcc<senta 



. -hypocot>rl 



After fertilization takes place in a 

 flower, the petals, stamens, and frequently 

 * h e stigmas of the pistil dry and generally 

 fall off. The embryo and endosperm de- 

 veloo and the ovule coats grow to accom- 

 modate the increased size of the seeds. 



The pod with us contents is the fruit. 



