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This rich flora reached its climax in the Carboniferous, and it will be more convenient to describe its varied types in the next chapter. RHIZOCARPS. In the shales of the Devonian are found microscopic spores of rhizocarps in such countless numbers that their weight must be reckoned in hundreds of millions of tons.
The Carboniferous was the age of lycopods and amphibians, as the Devonian had been the age of rhizocarps and fishes. The upridging of the Appalachians had begun and a wide continental uplift proved by the absence of Permian deposits over large areas where sedimentation had gone on before opened new lands for settlement to hordes of air-breathing animals.
Still further back the characters, afterwards separated in the club-mosses, mare's-tails, and ferns, were united in the rhizocarps, or, as some prefer to call them, the heterosporous filicinae."
It would seem that these aquatic plants culminated in this period, and in widely distant portions of the earth swampy flats and shallow lagoons were filled with vegetation of this humble type, either growing from the bottom or floating free upon the surface. It is to the resinous spores of the rhizocarps that the petroleum and natural gas from Devonian rocks are largely due.
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