Studies in the morphology of discomycetes
A hypothesis is proposed of the degeneration of the ascocarp by juvenescence from the multaxial form, represented nowadays in the genus Wynnea. The stipitate apothecium is considered to be a juvenile form limited to the main stem and first apothecium of the multaxial form. The clavate ascocarp of Geoglossaceae is considered homologous with the main stem, but with indirect development. Capitate, helvelloid and morchelloid forms of ascocarp are considered variations of the stipitate apothecium produced by reduction of marginal growth, increase of intercalary growth and indirect development. Juvenescence of the stipitate apothecium gives the variety of sessile forms. The hypothesis rests on the following facts : That the mature forms of ascocarp constitute a developmental series, the entirety being embodied in the development of the most complex. That degeneration is consonant with the biological value of smallness and precocity of the fruit body in subaerial environment. That there is even the requisite variation in the development of the ascocarp within specific limits at the present time. That small forms of ascocarp are characteristic of specialised habitats and the simplest are coprophytes, i.e. Ascobolaceae. That the construction of such simple forms corresponds to a juvenile stage in the development of a more complex ascocarp in allied species or genera, and there is no simple form known which cannot be so related. That 91 per cent, of modern Discomycetes have sessile apothecia, and the smaller forms preponderate. That the opposite case of Wynnea, 0·3 per cent, of modern Discomycetes, is explicable as vestigial in the least specialised stations of subaerial environment. That degeneration of the ascocarp is polyphyletic, and the evolution of Discomycetes conforms therefore in this respect with the universal principle of homoplasy. The first three facts clearly signify an evolutionary process, namely, results in accordance with an observed variation and a selective force. The bearing of the hypothesis on the classification of Discomycetes is briefly considered.