THE FOUR GREAT DIVISIONS 361 



The great majority of familiar plants belong to the highest 

 of these four divisions. Because these are the most famil- 

 iar plants, the first part of this book deals exclusively with 

 plants of this division, the division of seed plants. But you 

 would have a very imperfect idea of plant life if you knew 

 nothing about the plants belonging to the other divisions. 

 Also you would have a very imperfect idea of the seed 

 plants themselves if you understood nothing of the lower 

 plants, for the seed plants evolved from ancestors which 

 were like some of the lower plants of to-day. 



The four great divisions are the following : 



(1) T hallo phytes. These are the simplest plants and so 

 are regarded as the lowest from the standpoint of evolu- 

 tion. The word means thallus plants. Thallus means a 

 simple kind of plant body. It is not differentiated into 

 roots, stems, and leaves as are the bodies of the higher 

 plants. Seaweeds, toadstools, and the lichens you have 

 seen on rocks are all thallophytes, and there are many 

 others which are still more simple. The green threads you 

 have seen in stagnant water and in running brooks, the 

 green you have noticed on the bark of trees and where 

 water falls on stone or soil, this green is the green of sim- 

 ple thallophytes. 



(2) Bryophytes. The word means moss plants. Most 

 bryophytes are mosses, but some of them are liverworts. 

 The liverworts are often mistaken for mosses. The dif- 

 ference between them will be explained. 



(3) Pterido phytes. The word means fern plants and 

 most pteridophytes are ferns. There are certain other 

 plants, however, which do not look like ferns at all, yet 

 which also belong to this division. 



(4) S per mato phytes. The word means seed plants. You 



