THE PLANT IN ACTION. 257 



by the ovules, and comes in contact with the nucleus, 

 through the opening in the coats, at the apex of the 

 ovule (the micropyle). Afterward the embryo ap- 

 pears, just within the micropyle, with its radicle 

 pointing to the orifice. Before fertilization takes 

 place, the ovule prepares for it by the formation, at 

 the summit of the nucleus, of a special cell, called 

 the embryo-sac^ within which the embryo is formed. 

 It is supposed that the contents of the pollen grain 

 pass into the embryo-sac by osmotic action. In the 

 case of cone-bearing trees, the scales turn back, and 

 expose their inner surface at the time when the air 

 is filled with the pollen from the $ catkins, which 

 is thus enabled to act directly upon the naked ovules. 

 Then the scales close down, and remain till the seeds 

 are ripe, after which they again open, and thus permit 

 the seeds to escape. If you make sections of a pistil 

 when the pollen is in perfection with a microscope, 

 you may see these things for yourself. The spectacle 

 of a pollen-covered stigma is one of great beauty and 

 interest, even with a good magnifying-glass. After 

 fertilization, the flower withers, and the vigor of the 

 plant is spent in the growth and perfection of the 

 fruit. 



REPRODUCTION OF FERNS. All over the lower sur- 

 face of the prothallus (Fig. 352), cellular, pimple-like 

 bodies are formed. These projections consist of four 

 tiers of cells, with a canal running down the centre. 

 They project below the lower surface of the prothal- 

 lus, and, when mature, have an open mouth. The 

 canal leads to a basal cell (embryo-sac). These bodies 

 are the pistillidia or archegonia of ferns. 



ANTHERIDIA. These also are cellular projections, 



