104 REPRODUCTION 



duced in the stamen and escaping, and a large spore pro- 

 duced in the ovule, and not escaping. The small spore 

 (pollen) grows into a small male plant (male gameto- 

 phyte) : the large spore in the ovule grows in its place 

 inside the ovary in the pistil into a small female gameto- 

 phyte. The small male gametophyte produces two 

 sperms, one of which unites with the egg that is formed 

 in the female gametophyte. 



In other words, the old view thought of plants as 

 reproducing by the sexual method merely, as in the 

 higher animals. The new view states that seed-plants 

 have an alternation of generations just as the fern has. 

 It states that the seed plant has a generation that produces 

 spores, and these in turn produce another generation that 

 forms gametes. According to the old view the embryo in 

 the acorn is the child of the oak tree. According to the 

 new view it is the grandchild. 



5. What are the Proofs that there is an Alternation 

 of Generations in Seed Plants? It is not possible here 

 to give all the facts that convince the botanist that the 

 modern view is the right one, but there are two or three 

 things that may make it seem reasonable even to a 

 beginner. Everybody agrees that a new generation starts 

 when gametes unite. So when the nucleus from the pollen 

 tube unites with the nucleus of the egg cell, and this 

 fertilized cell begins to grow, we are sure we have a new 

 plant started. We can trace the growth of this plant at all 

 stages into the seed, and through germination, and on to 

 maturity. Furthermore, when these cells unite we have 

 the 2X chromosomes that we found in the sporophyte of 

 the moss and the fern; and this 2X condition of the nucleus 

 continues all through the life of the flowering plant. 



In the second place, when the pollen is formed, it is 

 formed very much like the spores in the fern. The 

 chromosomes are reduced to the X stage as they are in 

 the spore-formation of ferns. The pollen furthermore 



