202 



FIRST YEAR SCIENCE 



pollen grain of the right kind falls upon a stigma, it grows 

 and sends down a tiny tube through the style into the 

 ovary, where a little protoplasmic cell, called the egg cell, 

 has been produced. The essential parts of these two differ- 

 ent kinds of protoplasms unite and a new cell is formed. 



This new cell grows and divides into more cells, thus 

 forming the young embryo of a new plant. This embryo 

 is the living part of the seed and around it usually a great 

 deal of plant food is stored, so that when it begins to grow it 

 will have plenty of nourishment until it is able to develop 

 the roots and leaves necessary to prepare its own food. 



Embryos cannot be produced unless pollen grains and 

 egg cells unite, so it is absolutely essential that the right 



kind of pollen grains be brought 

 to the stigma. Some stigmas 

 are able to use the pollen grains 

 produced by the anthers of their 

 own flowers, but others can only 

 use pollen from other flowers 

 and other plants. It is there- 

 fore necessary that these pollen 

 grains be carried about from 

 flower to flower if fertile seeds 

 are to be produced. 



In some cases the pollen is 

 borne about by the wind, as in 

 the case of corn. In this way an exceedingly large number 

 of pollen grains are wasted, as can be seen by the great 

 amount of yellow pollen scattered over the ground of a 

 cornfield when the corn is in bloom. In the corn each 

 one of the corn silks is a pistil and a seed is produced at 

 its base if a pollen grain lights upon the stigma at its up- 

 per extremity. The flowers of walnut arid apple trees 

 are fertilized by wind-blown pollen. 



MINT FLOWER. 



