The inheritance of spore size in Coprinus sterquilinus

Abstract

Summary 1. An experimental study has been made of the inheritance of spore size in Coprinus sterquilinus, one of the homothallic Hymenomycetes. The character on which selection was based was length of spore. The original spore selections were made from six wild fruit bodies. In one series of experiments, each generation was propagated from the smallest spore which could be found; in another series of experiments, each generation was propagated from the largest spore which could be found. Selections from three fruit bodies were carried on for five generations, those from one fruit body for three generations, and those from two fruit bodies for two generations. Records were kept of the length of each mother spore, and of the mean length of the spores from the progeny fruit body of each monosporous mycelium. All spores were measured when dry with the Poynting Plate Micrometer. 2. The attempt to produce large-spored strains and small-spored strains in pure lines of Coprinus sterquilinus by the continuous selection of large and small spores respectively failed. No satisfactory evidence of the inheritance of individual variations in spore size was found. In this respect the spores of Coprinus sterquilinus resemble the seeds of the garden bean Phaseolus vulgaris nana investigated by Johannsen, the conidia of Phytophthora infestans investigated by Rosenbaum, and the spores of Pestalozzia Guepini and Helminthosporium teres investigated by La Rue. 3. There is considerable variation in the mean length of the spores produced by a fruit body at different times during the spore-discharge period. 4. Fruit bodies having small pilei produce smaller spores than those having pilei of the normal size or larger. 5. Since the mean size of the spores of different fruit bodies of one and the same species of Hymenomycete vary considerably, the spore size given by systematists for determining hymenomycetous species ought to be based on measurements of the spores of a number of fruit bodies obtained in different places. 6. The largest and smallest spores found were respectively 23·3 μ and 10·7 μ in length; the largest and smallest spores observed to germinate were respectively 22·8 μ and 12·6 μ in length. 7. The percentage germination of spores between 17·2 μ. and 23·3 μ. in length was 31·4; that of spores between 10·7 μ and 16·7 μ in length was only 16·2. Thus larger spores were found to germinate twice as well as smaller ones. 8. Frequency curves of spore length are presented for fruit bodies having modes for spore length of (1) 14·4 μ–15·3 μ, (2) 15·8 μ–16·7 μ, and (3) 20·0 μ–20·5 μ The relation between the forms of these curves and the nature of the variation in spore size in fruit bodies of Coprinus sterquilinus is discussed. 9. Miss Baden's conclusions (1) that spores of Coprinus sterquilinus germinate only in the presence of certain bacteria and (2) that they are not ready to germinate when they are shed have not been confirmed.