Reproduction in Multicellular Plants - 209 



The Filiceneae (Chapter 13). The Fili- 

 ceneae, or ferns, are all fairly well adapted to 

 land conditions. All have true root-stem-leaf 

 systems, equipped with well-developed vas- 

 cular (distributing) tissues (see later). More- 

 over, the filicenes have a regular alternation 

 of generations, but the sporophyte is domi- 

 nant relative to the gametophyte. Both the 

 gametophyte and sporophyte grow indepen- 

 dently in the holophytic manner. 



The Gymnospermae and Angiospermae 

 (Seed-bearing Plants, Chapter 31). The seed- 

 bearing plants include a countless variety of 

 conifers, cycads, and flowering plants. All 

 these plants have a highly vascularized root- 



stem-leaf system, which gives an excellent 

 adaptation to terrestrial conditions. The re- 

 productive cycle is also very well adapted to 

 the land habitat. In the regular alternation 

 of generations, the sporophyte has become 

 entirely dominant, and the gametophyte, 

 which is reduced to microscopic dimensions, 

 has become entirely dependent upon the par- 

 ent sporophyte (see later). 



THE LIFE CYCLE OF VARIOUS HIGHER 

 THALLOPHYTES 



Sexual reproduction appears first among 

 the Thallophyta, but these primitive plants 



PARENT COLONY 



EGG 

 SPERM 



ZYGOTE, ESCAPING 



ENCAPSULATED 



SPORES 



SINGLE SPORE 

 NEW COLONY^ 



Fig. 12-8. Reproductive stages in Oedogonium, one of the green algae. From 

 left to right: portion of the filament showing the large nonmotile egg and the 

 small motile sperm; sperm entering egg, just prior to fertilization; the zygote, 

 escaping through old cell wall; formation by meiosis of four swarm spores; 

 development of one swarm spore into new filament. 



