Sexual Reproduction in Flowering Plants 251 



The perisperm. In some seeds the tissue immediately sur- 

 rounding the embryo sac becomes much enlarged and accumu- 



FiG. i5g. Floral organs and development of fruit of bean : ^, side view of floral envelopes; 

 B, petals; C, stamens in two groups; D, stamen with anther; E, young pistil; F, young 

 pistil enlarged to show ovules ; G, H, I, and /, stages in the development of the fruit. 



lates food materials. In the mature seed this tissue resembles 

 the endosperm. Physiologically, endosperm and perisperm are 

 alike, in that they supply food to the growing embryo during the 

 germination of the seed. Corn cockle, spinach, and pepper seeds 

 have the food supply in the perisperm tissue. 



The seed. The final product of pollination and fertilization 

 is the seed. Its complete development ends the role of the flower. 

 During the development of the endosperm and embryo the wall 

 of the ovule, commonly called the integument, enlarges and may 

 change in various ways, sometimes forming a hard outer coat of 

 stone cells and an inner soft coat. The primary parts of a seed, 

 then, are (i) the seed coats, (2) the embryo, and (3) the endo- 

 sperm (or perisperm). When we plant a seed, we are placing a 

 small, partly developed plant, with a hmited supply of food, 

 under conditions in which it may continue its growth. Seeds 

 are discussed in more detail in the next chapter. 



