THE LARGER GROUPS OF PLANTS 29 



often borne in cones, as in the Coniferse, mostly needle- 

 leaved trees (pines, firs, etc.). The Seed Plants have 

 the most complicated internal structure of any plants. 



(2) The PTERIDOPHYTES, plants of the same grade 

 of organisation as the Ferns, and possessing, like the 

 Seed Plants, stems, roots and leaves, and a well-devel- 

 oped internal water-conducting system, but reproducing 

 themselves not by seeds, but by very minute bodies 

 called spores. These include the Ferns, Olubmosses, 

 and Horsetails. The living forms of the two last- 

 named groups represent a very small proportion of 

 the plants belonging to these groups, which flourished 

 in certain past ages, and which, often growing to the 

 size of trees, are preserved as fossils in the coal measures 

 and other rocks. In the same rocks are preserved 

 forms which are intermediate between the Pteridophytes 

 and the Seed Plants. These formed seeds, but seeds 

 which were different in structure from the seeds of 

 existing plants. 



(3) The BRYOPHYTES, including the Mosses and the 

 Liverworts, also reproducing themselves by spores, but 

 much smaller on the whole than the Pteridophytes, 

 and with a less well-developed water-conducting system, 

 or none at all. The Mosses and some of the Liverworts 

 have distinct stems and leaves, but other liverworts 

 have none, the plant body consisting of a flat thallus, 

 usually a branched ribbon-shaped structure, rather 

 like an indefinitely growing leaf. These forms are 

 mostly only able to live in relatively damp places, 

 though the majority are land plants. 



(4) The ALG^J, plants living mostly in water, and 

 able, like the previous groups, to form organic sub- 

 stances from inorganic. They all contain chlorophyll, 

 but some of them, the red and brown seaweeds, for 



