268 A TEXTBOOK OF GENERAL BOTANY 
History as told by fossils. ‘The oldest plant fossils were all 
water plants with a simple organization, and belonged to that 
great composite group known as thallophytes. Thallophytes are 
not differentiated into stems and leaves. Flowering plants are 
relatively recent arrivals upon the scene. Between the age of 
thallophytes and the recent age of flowering plants there was 

Fig. 245. Erosion on a mountainside (Taal Volcano, Philippine Islands) 
a succession of many floras, the dominant elements of which 
showed an ever-increasing complexity. In the Carboniferous Age 
the forests contained trees that were a hundred or more feet in 
height, lacked both flowers and seeds, and reproduced by means 
of single cells called spores. No such trees have existed for 
many ages. In the Carboniferous Age there were also fernlike 
plants with seeds; these likewise died out ages ago. In general 
the dominant groups of the ancient land floras have either disap- 
peared or are unimportant constituents of our present flora. 
The fossil record shows that in animals also there has been 
a development from the simple to the complex, and that mammals 
an 
