258 



THE CONTINUITY OF THE RACE 



theridia) produce a huge number of ciliated male gametes or sperms. These, 

 when released from the antheridium, are able to swim in water films 

 provided by rain and dew and so reach the egg within the female sex 

 organ. The union of a male gamete with the egg produces a diploid zygote 

 that develops into a diploid sporophyte plant. This sporophyte genera- 



spore copiule 



mgiurv i 



sporophyte y 



re mole 

 gomelophyle 



*. sperm ^^ 



Fig. 17.4. Alternation of generations in the Bryophyta. The life cycle of a moss. (Modified 

 from Turtox chart, courtesy General Biological Supply House, Inc.) 



tion is not free-living but lives as a parasite on the green gametophyte. 

 It forms a bulblike foot that grows down into the gametophyte tissues to 

 obtain nourishment, and then sends up a stalklike structure that develops 

 a conspicuous capsule at its distal end. The foot, stalk, and capsule, which 

 lack chlorophyll and are usually somewhat longer than the leafy gameto- 

 phyte stem from which they extend, constitute the sporophyte generation 

 that begins with the zygote. 



Spore formation. Once the sporophyte tissues are complete, spore 

 mother cells within the capsule undergo maturation and repeated asexual 



