228 EVOLUTION OF PLANTS 



their own in modern times better than any other Coni- 

 fers. At present, these are decidedly the prevailing 

 types of coniferous trees, but even these, in most re- 

 gions, show signs of yielding to the encroachment of 

 the angiospermous trees. 



While various fossils from the Carboniferous and early 

 Mesozoic formations have been assigned to the Angio- 

 sperms, it is not until the later Cretaceous is reached 

 that undoubted remains of these plants occur. Here 

 are found unmistakable traces of both Monocotyledons 

 and Dicotyledons, but most of the earliest remains are 

 of such character as to throw little light upon the 

 relation which these two groups bear to one another. 

 Among the earliest forms of which recognizable re- 

 mains are found, are palms and screw-pines among 

 the Monocotyledons, and birches, willows, and poplars 

 among the Dicotyledons. It need not necessarily follow 

 that these are the most primitive of the Angiosperms, 

 although they are doubtless among the more primitive 

 types. Their preservation is simply due to the fact 

 that their tissues were firm and resisted decay long 

 enough to leave clear impressions. Most of the living 

 Angiosperms which are considered as probably the most 

 primitive, especially among the Monocotyledons, have 

 extremely delicate and perishable tissues, which, as in 

 the case of algse, could hardly be expected to leave 

 recognizable fossil remains. 



In the later Tertiary rocks, remains of Angiosperms 

 became very abundant, and most of the existing groups, 

 especially of Dicotyledons, can be distinguished. It is 

 evident that at last a type of plants has been evolved 

 which is rapidly crowding out the less perfect types 



