PLANT GROUPS 



261 



of them you know very well, for they are the ferns. You 

 know that ferns develop leaves and stems and roots, and 

 they have much larger bodies than do the mosses and liver- 

 worts (see Fig. 100). In fact, you know that some of the 

 ferns became trees, 

 which you may have 

 seen in greenhouses 

 (see Fig. 101). 



Why were ferns 

 able to become larger 

 than mosses? The 

 answer is that they 

 had developed some- 

 thing new, and that 

 was woody fibres. 

 These woody fibres 

 not only make a 

 more rigid body, but 

 their chief value 

 came from the fact 

 that they carry 

 water. It was like 

 putting a system of 

 water-pipes into the plant. By means of these water-pipes 

 the water entering through the roots can be carried rapidly 

 and directly to leaves far above the ground. In this way 

 plants could become larger, and trees became possible. 



You will remember that you have seen yellowish or black- 

 ish dots on the under-surface of many fern-leaves. These 

 are made up of little vessels that produce small bodies 

 that are called spores. It is by means of these spores that 

 new fern-plants are produced. There are no seeds yet. 



FIG. ioi. Tree-ferns. 



