278 



REPRODUCTION OF HIGHER PLANTS 



clei 





ote 



the process oi 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 ffoing 



In the process of fertilization in a flower a 

 sperm nucleus unites with an egg cell nucleus from thc plant thrOUgh the 

 to form the embryo of the future plant. The 



:J 



..remains of stigma 

 ana st^I 



.jJlacenta 



cropyle 



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. 



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 growls rapidly and 

 stores the future food supply for the 

 embryo. As the embryo develops 

 into a manv-celled structure, dif- 

 ferentiation of the cells sets in and 

 the first root or hypocotyl, the first ^/J:- J/^^^^^^^^^ 



bud or Vlumule, and the seed leaves the stigmas of the pistil dry and generally 



^ ' fall off. The embryo and endosperm de- 



Or cotyledons are formed. The en- veloo and the ovule coats grow to accom-, 



^ . modate the increased size of the seeds. 



dosperm develops at the same time. The pod with its contents is the fruit. 



jlum-ule 



hypocotyl 



