The Angiosperms 149 



of their structures is extraordinarily great, illus- 

 trating again their remarkable powers of adaptation. 

 Some of them are tiny, almost microscopic water 

 plants of extraordinarily simple structure; others 

 are humble weeds, completing their whole life in 

 the course of a few weeks, while still others are 

 giant trees, living hundreds of years. With all this 

 extraordinary variation in size, form, and habit, the 

 fundamental structure of the flower, the character- 

 istic mark of the angiosperms, is very uniform, 

 but is so different from that of any gymnosperms 

 as to make the origin of the angiosperms a matter 

 of great uncertainty. 



Angiosperms Absent from the Early Rocks 



While the ferns and gymnosperms have left abun- 

 dant and well-preserved fossil remains whose nature 

 is unmistakable, of the angiosperms, except in the 

 later geological formations, only scanty traces are 

 discernible, and these are often very uncertain in 

 their nature. While a good many fragments of 

 leaves and stems from Paleozoic and early Meso- 

 zoic rocks have been assigned to angiosperms, these 

 fragments in most cases are very poorly preserved, 

 and their real nature is, to say the least, problem- 

 atical. The tendency among recent students of these 

 fossils is to relegate them either to pteridophytes or 

 gymnosperms. 



It is not until the later Mesozoic formations 

 are reached that unmistakable remains of angio- 

 sperms are found. From the Cretaceous upward 



