APPENDIX A 



609 



in Chap. XVII. Stalked organs, some bearing antheridia and others archegonia, 

 are formed at certain times. The sperm produced in the antheridia are flagellate 

 and motile; when the surface of the liverwort is wet, they can swim in the water 

 film to reach and fertilize the eggs in the archegonia. The resulting zygote grows 

 into a small sporophyte, which produces spores that germinate and give rise to a 

 new gametophyte generation — the thallus already described. 



Fig. A.ll. Marchantia polymorpha, a common thallus liverwort. Upper left, gametophyte 

 with antheridial heads; lower left, gametophyte with gemma cups from which asexual buds 

 (gemmae) are issuing; right, gametophyte with archegonial heads. (Photos by Prof. E. B. 

 Mains.) 



In addition to this reproductive cycle, Marchantia reproduces asexually in 

 two ways. One results from the mode of growth; the growing point advances and 

 from time to time divides, while the plant dies from the rear. When death reaches 

 a fork, two separate thalli are formed from one. The second method is the pro- 

 duction of tiny, oval, flat buds in small cups on the upper surface. These buds, 

 called gemmae (Fig. A.ll), break free and are splashed away by rain to grow into 

 new gametophyte plants. 



The leafy liverworts look like mosses but have definite upper and lower surfaces 

 like the thallus types, instead of stems with radial structure like mosses. They 

 also differ from mosses in having no vascular tissues, in having leaves without 



