182 



PHENOGAMS AND CRYPTOGAMS 



337. Fertile and sterile fronds 

 of the sensitive fern. 



larger and more highly developed. In the seed-bearing 

 plants the sporophyte generation is the only one seen by the 

 non-botanist. The gametophyte 

 stage is of short duration and the 

 parts are small: it is confined to the 

 time of fertilization. 



352. The sporophyte of the seed- 

 plants, or the plant, as we know it, 

 produces spores which, however, are 

 not visible to the naked eye. The 

 spores are of two kinds: microspores 

 borne in tissues called sporangia 

 which forms part of the anther; and 

 macrospores which 

 are present in the 

 pistil. The microspore developes into the 

 pollen-grain. The macrospore develops 

 in the ovule into an embryo-sac, which 

 contains the egg nucleus. The germi- 

 nated pollen-grain constitutes the com- 

 pletely developed sterile gametophyte. 

 The fully developed embryo-sac constitutes the fertile gam- 

 etophyte. Fertilization occurs, and the sporophyte is again 

 produced. This new sporophyte 

 develops farther and we have the 

 embryo plant formed in the seed. 

 This may remain dormant for a 

 time, and when germination 

 occurs the visible sporophyte plant 

 is produced. This in turn produces 

 microspores and macrospores, and 

 the cycle is again complete. The 

 alternation of these phases in the 

 plant's life history is known technically as alternation of 

 generations. 



338. A sac-like indusium. 



339. Prothallus of a fern. Enlarged. 

 Archegonia at a; antheridia at b. 



