196 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



comparable to the resistance offered by the same vegetation on a nearly flat land, 

 where the water of a heavy rainfall is held back sometimes to a considerable 

 depth by the dense growth and tangle of fallen vegetation, thus extending the 

 swamp conditions far inland. Many coal swamps were in vast deltas. 



"Semiaquatic Vascular Plant Growth. 



"The examination of the structure, development, and affinities of the principal 

 plant types found associated with the Paleozoic coals points to the conclusion 

 that many of them, especially among the lepidophytes,' grew under conditions 

 characteristic of swamps, a large number of them being adapted to growth 

 in standing water. Pontonie has pointed out that the enlarged bases of the boles 

 of many of the old Sigillariae and Lepidodendreae appear precisely comparable 

 to the basal enlargements of the black gum, Jussiaa, the bald cypress, and many 

 other types growing in water-covered swamps of tropical and warm temperate 

 climates at the present time. The lateral traces or "parichnos" of the leaf- 

 scars were long ago recognized by Renault as points of air contact with the tracts 

 of lacunose assimilation parenchyma (aerenchyma) in the thick cortices of the 

 trunks. Subsequently Gothan and Pontonie have pointed out that these twin 

 leaf-scars, often so conspicuously enlarged on the old trunks, where they sometimes 

 measure nearly a centimeter in length, are in effect lenticels, or breathing surfaces, 

 developed to afford a better air-supply to tissues where the water cover of a 

 swamp deprives the root system of access to the atmosphere. Potonie- has shown 

 also that Sigillaria developed giant "knees," so-called pneumatophores, similar 

 to those developed by the bald cypress when growing in water, and similarly 

 provided with breathing-pores. The height to which some of the trunks of 

 Sigillaria are enlarged justifies the belief they may have grown in some instances 

 in a normal water cover nearly 4 feet in depth. It has also been conclusively 

 shown by Grand 'Eury' that most of the larger types were adapted to survive 

 rapid deposition about their trunks or rhizomes. Evidence that the commonly 

 associated plants also were suited to an aquatic environment is found in the 

 shallow root system of Stigmaria, which extended far out horizontally on or 

 near the surface of the peat in order to avoid the toxic air-exhausted deeper 

 layers; the occurrence of gum-canals in the rootlets of the fern trunk, Psaronius, 

 the hollow interior of the Stigmaria appendages and the absence of root-hairs, 

 distinctly pointing to an aqueous habitat; the presence of air-chambers in the 

 Calamarian roots, and the development of subaerial roots in many types; the 

 presence of mycorrhiza, as described by Osborn, in the roots of Cordaites, indicat- 

 ing a peat substratum for the plant; the air-charnbers provided for the flotation 

 of many of the seeds; and the production by many of the lycopods and Calamarian 

 types of two kinds of spores, requiring an aqueous environment in which the two 

 kinds could more certainly come together in a place sufficiently wet to insure 

 fertilization.* 



* See Grand 'Eury, C, Du Basin de La Loire, Compt. Rend., 8th Cong. Geol. Internal., 



Paris, 1901, pp. 521-538; Pontonid, H., Entstehung d. Steinkohle, 5th ed., 1910, p. 173. 

 ' Potoni6, H., op. cit., pp. 176, 181. 

 ' Grand 'Eury, C, Sur le caract^re paludeen des plantes qui ont form6 les combustibles 



fossiles de tout age, Compt. Rend., vol. 138, 1904, p. 666. 



* The rapid decrease, almost amounting to disappearance, of the greater number of the 



very large spored lycopods during Conemaugh time (early Stephanian) was no doubt 

 due to failure of fructification caused by periods of relative drought and reduction of 

 the water-surface, such withdrawal of the water being plainly indicated by the preva- 

 lent pseudoxerophytic characters observed in the swamp plants of the period. 



