THK WORK OF FLOWERS 



291 



place, the egg does not 

 ordinarily develop; 

 hence we see why 

 pollen is necessary in 

 order to set seed. If 

 we examine various 

 flowers with a hand- 

 lens, we find the pol- 

 len deposited in a par- 

 ticular spot, which is 

 provided with brushes, 

 hairs or sticky sub- 

 stances in order to 

 retain it. This spot is 

 called the stigma (see 

 Fig. 161). What hap- 

 pens if we remove the 

 stigma? Remove the 

 stigma before the bud 

 is open, being careful 

 not to injure the other 

 parts of the flower. 

 Do not protect the 

 flowers from insects, 

 but rather assist pol- 

 lination by placing 

 pollen on the flower. 

 Do you find that flow- 



164. Embryo sac of a Lily, showing the union of 

 the nucleus from the pollen- tube (pn) with the 

 egg(e): the second pollen -tube nucleus (spn) 

 unites with two endosperm pro-nuclei (fnd), 

 which multiply and form the endosperm: (ant) 

 antipodal cells, (nr) nurse nuclei which help 

 nurish the egg, etc., (p) pollen-tube. 



