496 



General Botany 



T. D. A . Cockerell 



Fig. 308. Fossil flower from the Tertiary shales at Florissant, 

 Colorado. 



internal structures of the plant are preserved. As animal re- 

 mains are preserved in the same way, we have in the rocks a 

 record of the plants and animals of the past. These petrified 

 plant and animal remains and the plant and animal imprints 

 from former geological ages are cdM^d fossils. 



Fragmentary nature of fossil record. Present-day observa- 

 tions on the fate of fallen leaves and of other plant organs show 

 that they usually decay and disappear within a few months. 

 Fossils are being formed at the present time only in lakes, in 

 bogs, in muddy estuaries, and in a few other exceptional situa- 

 tions. It is only by rare chance that upland plants leave a 

 record. We should therefore expect to find the geological record 

 of plants very fragmentary. 



The Pteridophytes and their near relatives, being plants of low 

 grounds, swamps, and bogs, were situated in the most favorable 

 habitats for preservation and their record is more complete, 

 perhaps, than that of any of the groups of land plants. 



The record of plant groups below the Pteridophytes is very 

 scant for two evident reasons. The simple thalloid plants 



