THE PAST HISTOKY OF PLANTS. 231 



grasses, each specially adapted for some one 

 particular situation. 



Only the closest individual study can give any 

 adequate idea of this immense diversity of 

 plants in nature. 



The geological history of the world shows us 

 that the development of plants has been slow 

 and progressive. In the earliest rocks (of which 

 an account is given in another volume of this 

 series), we get few traces of any plants but the 

 lowest : so that at that time it is probable none 

 but seaweeds and their like existed — cellular 

 plants which contain hardly any parts solid 

 enough for preservation. By the age when the 

 coal was laid down, however, ferns, horsetails, 

 and many gigantic extinct plants with solid 

 stems had begun to exist ; but few or no flower- 

 ing plants, except conifers, had yet been de- 

 veloped. Later still came the true flowering 

 plants, with covered seeds, at first in simple and 

 antiquated forms, but becoming more complex 

 as birds, mammals, and flying insects of the 

 flower-haunting types were developed side by 

 side with them to visit and fertilise them or to 

 disperse their seeds. Succulent fruits, of course, 

 could only arise when tribes of fruit-eaters had 

 been evolved to assist them ; while such special 

 bee-fertilised types as the sage group, and such 

 complex forms as the orchids and composites, 

 requiring the aid of highly-developed insects, 

 are of extremely recent evolution. Plant and 

 animal life have continually reacted upon one 

 another. 



