. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARATTIACEAE 523 see, the comparison is confirmed by reference to the petrified stems known as Psaronius. This consideration will justify our drawing together the modern and the fossil forms into a comparison with a view to tracing probable phyletic changes in the structure of the sorus, and a recognition of an original The definitely circumscribed sorus appears to be a characteristic of the Marattiaceae, both ancient and modern. The form of the sorus varied from circular to elongated, both in
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARATTIACEAE 523 see, the comparison is confirmed by reference to the petrified stems known as Psaronius. This consideration will justify our drawing together the modern and the fossil forms into a comparison with a view to tracing probable phyletic changes in the structure of the sorus, and a recognition of an original The definitely circumscribed sorus appears to be a characteristic of the Marattiaceae, both ancient and modern. The form of the sorus varied from circular to elongated, both in the fossils and in living forms: there is no distinctive stratigraphical evidence to show which type was the prior, but in the majority of the early fossils the sorus is circular, with a small number of sporangia. Further, the Pecop- terid is a relatively narrow-leaved type, while the leaves of Danaea and Kaulfussia are broad : if a widening of the leaf took place, followed by extension of the sorus, the result would be as in 7-1 7-, -, 'r -i . • Danaeites saraeftontanus. Stur. From the upper car- Danaea Or Danaeites \ if aDStrlC- boniferous of the Saar district. A =a fertile segment of +,*«„ .r+t,ft nT .j n • r m j the last order. .6*=transverse section throughi two adioin- tlOn Of the elongated SOn followed ing son, or the hollow impression of them C = below a alcn rho i-ecult- ho oc ,'n sorus of sixteen sporangia; above the impression of it. alSO, tne result WOUld De as in (After Stur. From Engler and V™t\, Nat. Pjlanzenfam.) Kaulfussia. The evidence of the partial septa in Danaea, and the irregularity of size and segmentation of the sporangia throughout the family, accords with the suggested extension of an originally circular sorus with few loculi to produce the more or less elongated sori of the living forms with more numerous loculi. A further point for discussion is the original relation of the sporangia to one another in the sorus. Among both ancient
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