COMMENCEMENT OF LAND HANTS. 45 



On the other hand, it is not easy to admit such repeated 

 risings and sinkings of surface as would be required, on 

 this hypothesis, to form a series of coal strata. Perhaps we 

 may most safely rest at present with the supposition that 

 coal has been formed under both classes of circumstances, 

 though in the latter only as an exception to the former. 



Upwards of three hundred species of plants have been 

 ascertained to exist in the coal formation ; but it is not 

 necessary to suppose that the whole contained in that 

 system are now, or will be, distinguished. Experiments 

 show that some great classes of plants beoome decompos- 

 ed in water in a much less space of time than others, and 

 it is remarkable that those which decompose soonest, are 

 of the classes found most rare, or not at all, in the coal 

 strata. It is consequently to be inferred that there may 

 have been grasses and mosses at this era, and many spe- 

 cies of trees, the remains of which had lost all trace ot 

 organic form before their substance sunk into the mass ot 

 which coal was found. In speaking, therefore of the vege- 

 tation of this period, we must bear in mind that itmay have 

 comprehended forms of which we have no memorial 



Supposing, nevertheless, that, in the main, the ascer- 

 tained vegetation of the coal system is that which grew 

 at the time of its formation, it is interesting to find that 

 the terrestrial botany of our globe begins with classes of 

 comparatively simple forms and structure. In the ranks 

 of the vegetable kingdom, the lowest place is taken by 

 plants of cellular tissue, and which have no flowers, 

 (cryptogamia,) as lichens, mosses, fungi, ferns, sea- weeds. 

 Above these stand plants of vascular tissue, and bearing 

 flowers, in which again there are two great subdivisions ; 

 first, plants having one seed-lobe (monocotyledons,) and 

 in which the new matter is added within (endogenous,) 

 of which the cane and palm are examples ; second plants 

 having two seed-lobes (dy cotyledons,) and in which the 

 new matter is added on the outside under the bark, 

 (exogenous,) of which the pine, elm, oak, and most of the 

 British forest-trees are examples ; these subdivisions also 

 ranking in the order in which they are here stated. Now 

 it is clear that a predominance of these forms in succes- 

 sion marked the successive epochs developed by fossil 

 geology; the simple abounding first, and the complex 

 afterwards. 



Two-thirds of the plants of the carboniferous era are 



