352 Introduction to Botany. 



seldom possible. In the Silurian rocks, however, have been 

 found the silicified remains of a large plant which appears 

 to be closely related to the modern Laminarias ; Fuais also, 

 described on page 275, being a near relative. Dawson 

 named it Nematophyton, and wrote of it : " When we con- 

 sider that Nematophyton was a large tree, sometimes attain- 

 ing a diameter of two feet and a stature of at least twenty 

 before branching, that it had great roots and gave off large 

 branches, and that it was an aerial plant, probably flourish- 

 ing in swampy flats, that its seeds are so large and complex 

 as hardly to be regarded as mere spores, we have evidence 

 that there were in this early Paleozoic period plants scarcely 

 dreamt of by modern botany." 



221. Devonian Plants. — In the rocks of the Devonian 

 period we find remains of representatives of nearly all 

 forms of the higher Cryptogams, the tree ferns (Fig. 192) 

 being of most frequent occurrence. In the forests of the 

 Devonian occurred near relatives of the modern Lycopods 

 or ground pines, and a genus of Gymnosperms, known as 

 Cordaites, having leaves about 50 centimeters long (Fig. 

 192). All conditions were favorable for an abundant 

 growth of plant life, and the waters must have teemed 

 with forms which have left no impression in the rocks. 

 The greatest petroleum-bearing strata in the world belong 

 to the Silurian and Devonian periods, and since the source 

 of petroleum, natural gas, etc., is evidently to be attributed 

 to plant as well as to animal remains, the amount of or- 

 ganic materials built up by the plants of those periods is 

 incalculable. (It will be remembered that animals obtain 

 their food already organized from plants.) 



222. Carboniferous Plants. — The Carboniferous period 

 is of particular interest because the remains of its vege- 

 tation constitute the chief part of the coal supply. The 



