124 



HARDWICKE'S SCIENCE-GOSSIP, 



affords some indications of the prevailing climates, 

 and we are at once struck by the somewhat tropical 

 appearance of the plant remains of the Carboniferous 

 period, which evidently betokens a warmer and 

 more equable climate than is now experienced in 

 many of the countries where coal is found. Wondrous 

 changes in the distributions of temperature must have 

 taken place since the days when Novaya Zemlya and 

 Spitzbergen were covered with the dense growth of 

 the coal period. 



It may be that the normal temperature of the earth 

 itself was then somewhat warmer than it now is, and 

 also that the atmosphere was more highly charged 

 with aqueous vapours than at present, producing a 

 climate highly favourable to the development of a 

 Cryptogamic flora ; and the Carboniferous period may, 



unlikely that some of the fragmentary fronds may 

 have belonged to arborescent forms. Schimper 

 argues indeed that since the arborescent ferns of New 

 Zealand are often without fructification, and that the 

 majority of the coal-measure ferns are similarly 

 destitute, and also belong to families which are rich 

 in living arborescent species, therefore there may have 

 been a great abundance of these tree-ferns during the 

 Carboniferous age. The number of ferns that have 

 been obtained from the coal measures is very large ; 

 at least 250 species are known, whilst Europe to-day 

 possesses only sixty indigenous species. Before enter- 

 ing into further details as to the ferns of the coal 

 measures, it will be well for us to notice the general 

 characters of this order of plants, especially with a 

 view to the recognition of microscopical specimens. 



Fig. 84. — Sporangia of Ferns. 

 a, Hymetwphylluin Tun- 

 bridgense ; b. Fossil ditto, 

 Oldham. 



Fig. 83. — Rachiopteris. Transverse section of Fern-stem. X 26 diam. 



without much exaggeration, be characterised as the 

 Age of Cryptogams. 



The Flora. — We will now examine somewhat in 

 detail the more prominent plants which have been 

 recovered from the chaos of the coal fields. Amongst 

 the most beautifully preserved of the Carboniferous 

 plants are numerous Ferns, closely resembling in 

 general appearance existing species. Various genera of 

 Equisetacese (Horsetails), Lycopodiaceaj (Club mosses) 

 and Coniferae, all of which have their analogues still 

 existing, and side by side with them, are other plant 

 remains of more or less doubtful afifinities. 



The Ferns. — The ferns of the coal measures were 

 perhaps mostly herbaceous, and of the ordinary size 

 of the common European species ; not more than two 

 or three undoubted arborescent species, I believe, 

 have been found in this country, and of them only 

 portions are known for certain, although it is not 



The ferns form a group of plants which is acro- 

 genous, that is, it increases by successive additions at 

 the apex. ExternaUy, ferns are seen to have a 

 Caudex or Rhizome, which creeps below the surface 

 or upon it, and has very much of the appearance of 

 a root, but it is really a prostrate stem, and from this 

 spring the leaves or fronds which are borne on a 

 stipes or stalk. 



The caudex is sometimes very large as well as 

 erect, and rises like the trunk of a tree, it is nearly 

 uniform in circumference throughout its length, and 

 is marked symmetrically by the scars produced by 

 the bases of decayed fronds. 



Internally, the structure of a fern consists of a 

 central medulla or pith, which in some species is 

 surrounded by a regular cylinder of scalariform tissue ; 

 in others the vascular bundles are scattered about 

 through the whole mass of tissue in detached bundles, 



