THE EVOLUTION OF THE PLANT-WORLD 17 



The widespread and luxuriant flora of the Coal- 

 Measures seems to have differed little in general char- 

 acters from that of the Devonian period. Whole beds 

 of coal are formed of the leaves of CordaUes. Lepido- 

 dendron, that genus of gigantic club-mosses which finds, 

 perhaps, its nearest living representative in the humble 

 aquatic Isoetes, is one of the best known of Coal-Measure 

 fossils, with its ally Sigillaria and the giant horsetails, 

 Calamites; while it is now recognised that the majority 

 of the so-called fern fronds belong to the Pteridospermece. 

 At the same time, we have specimens from our English 

 Coal-Measures of undoubted ferns, the sporangia of 

 which are destitute of an annulus, while the stele (or 

 vascular axis of their leaf -stalks) is markedly H-shaped 

 in transverse section. For these generalised types, 

 combining characters of the Ophioglossacece, Osmun- 

 dacecs, and Marattiacea, the name Primofilices has been 

 suggested. In spite of the proof that many sporangia 

 supposed to belong to ferns are truly the microsporangia, 

 or pollen-sacs, of Pteridospermecs, it is possible that true 

 Marattiacece, ferns with stipules at the base of their 

 smooth-stalked, much-divided fronds, with a complex 

 stem-structure, and with their sporangia united in 

 " synangia," did contribute to our Coal flora. 



The club-mosses, though represented by gigantic 

 tree-like forms, the stems of which had that power of 

 increasing in diameter by secondary growth once thought 

 peculiar to flowering plants, also included herbaceous 

 forms as small as their modern representatives. Some 

 of these, such as Miadesmia, in spite of their reduced 

 size, exhibit a great advance in the evolution of their 

 reproductive system producing true seeds though 

 in other characters closely resembling Selaginella. 



It is possible that true Conifers and Cycads may be 

 represented in European Carboniferous rocks by such 

 fossils as Ullmannia, Noeggerathia, and Pterophyllum; 

 and the coniferous nature of the Permian Walchia is 

 unquestioned. 



Obviously the flora of the Palaeozoic age was not 

 exclusively cryptogamic; although, perhaps, many of its 

 primitive seed-bearing plants, like Ginkgo and the 

 Cycads to-day, may have retained that relic of an 

 aquatic ancestry, the spirally-coiled spermatozoid within 

 the pollen-tube ." 



B 



