332 PAL/EONTOLOGY 



tophyte] being the larger and more important plant, the 

 asexual (sporophyte) being short-lived and always attached 

 to the gametophyte : hence it is commonly taken for a 

 mere fruit of the latter. The male and female repro- 

 ductive cells can only function in a liquid environment, 

 hence the gametophyte can only live in damp situations ; 

 but the asexual spores produced by the sporophyte are 

 adapted to resist drought and to be disseminated by the 

 wind. The plant-body of the Bryophyta shows greater 

 differentiation in its cells than the Algae, and the 

 beginning of formation of vessels, but it never attains a 

 truly woody structure and is hence almost unknown in 

 the fossil state. 



3. Pteridophyta. In this grade (Ferns, etc.) there is 

 a reversal of the relative importance of sporophyte and 

 gametophyte. The former is now the larger and longer- 

 lived, it is well differentiated into root, stem, and leaf, and 

 has woody and other tissues capable of preservation in the 

 rocks. It can live in dry soils, but must not be far from 

 water. The spores are borne in spore-cases (sporangia) 

 usually on the ordinary leaves, sometimes on special 

 leaves (sporophylls\ and are wind-scattered, germinating 

 into gametophytes in damp places. 



The gametophyte is very small, delicate, as simple in 

 structure as any of the Bryophyta, and short-lived. Some- 

 times the sporangia and spores are of two kinds, large 

 megaspores from which female gametophytes grow, and 

 small microspores which produce males. 



4- Spermaphyta (Seed-Bearing Plants). In these, 

 the highest plants, the megaspore germinates, forms a 



