DEVELOPMENT OF THE SEED 



287 



lying one of these develops, the others perishing. So the 

 ovule comes to have one megaspore, which is retained in 

 the ovule tissues. A little later this megaspore develops 

 an egg in connection with a greatly reduced archegone, 

 and a very immature gametophyte, in the following 

 manner: 



The nucleus of the megaspore divides into two, which 

 move to opposite poles of the megaspore cavity; here 

 they divide twice resulting in four nuclei at each pole; 

 then a nucleus from each pole (the so-called polar nuclei) 

 moves to the center, where they ultimately unite. At 

 the upper (micropylar) end one of the (naked) cells 

 becomes the egg, accompanied by two companion cells 



Fio. 160. Ra- 

 nunculus (pistil 

 and seed). 



FIG. 161. Ranunculus (de- FIG. 162. Pol- 



velopment of ovule). len, tubular anthe- 



rid and sperms. 



("synergids")- At the lower end are the antipodal 

 nuclei (or cells). About this time any pollen cell (micro- 

 spore) that may have fallen upon the soft tissue of the 

 carpel stigma germinates there producing its most 

 reduced gametophyte, and a tubular antherid (pollen 

 tube). The latter penetrates the soft stigma tissues 

 toward the ovary cavity, carrying down the two sperms. 

 When the tubular antherid reaches the ovule it enters 

 the little pore (micropyle) at the summit of the indusial 

 coats, and penetrates the ovule to the egg where one of 

 the sperms then unites with the egg, this constituting 

 fertilization. The zygote now divides repeatedly and 



