SPERMATOPHYTA 75 



6. How did the climate of the Tertiary differ from that of 

 the Pleistocene and the present ? What was the chief cause 

 of this difference ? Give examples among plants that show that 

 this climatic change took place. 



Order F, Gnetales 



This group of small trees or shrubs consists of three living 

 genera, including P^j^hedra of the desert regions of both hemi- 

 spheres. They differ from other gymnosperms and show some- 

 what angiospermous tendencies in certain structural characters 

 of the wood and in some flow^er-like features of the reproductive 

 organs. 



Fossil record of the order would have high interest but so far 

 has not been forthcoming. 



1. What are the Gnetales? 



2. What fossil record have they? 



SUBDIVISION B, AXGIOSPERM.^ 



As the mammals represent the culmination of the much 

 branched animal line of ascent, so the angiosperms contain the 

 plants of highest rank. This group, the latest to come upon 

 the earth, comprises over half of all known living species of 

 plants. It is the angiosperms which clothe most of the earth 

 with vegetation ; in every climate and at almost all altitudes 

 they nearly always compete successfully with all other vegetal 

 types. They not only cover much of the earth with forests and 

 grasses, flowering herbs and shrubs, but many species (e.g. 

 water-lily, duckweed) have invaded the fresh-water realm of 

 the algcC with wonderful success. Though very few angiosperms, 

 as the eel-grass (Zostera), have tried to dispute with algae a 

 habitat in the sea, they are the only group to have invaded the 

 sea at all, for the gymnosperms, ferns and mosses have no 

 representatives there. 



The members of the Angiospermae are commonly known as 



