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Published online by Cambridge University Press: 06 July 2012
In a general survey of the pinna-traces of Ferns (Davie, '14), the results of which have been summarised in tabular form (loc. cit., p. 354), two main types of pinnatrace were described and contrasted. In the one—the “extramarginal”—the pinnatrace leaves the back of the hook formed by the incurved edge of the leaf-trace; in the other—the “marginal”—the outwardly directed margin of the leaf-trace is simply nipped off as the pinna-trace. The more primitive Ferns in the evolutionary scale, and the first leaves of both primitive and advanced Ferns, exhibit the marginal type of pinna-trace; the extramarginal type of pinna-trace is found in those Ferns which stand midway between the extreme types in the system of classification, and in some advanced forms.