Reproduction in Thallophytes, with Special Reference to Fungi

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Abstract
A critical review of recent factual and theoretical contributions in the fields of sexuality and genetics of thallophytes, especially fungi, is followed by a proposed clarification of concepts bearing on the phenomena of reproduction in this division of plants. The existing confusion with reference to the concepts sex, sexuality and sexual reproduction which appears in its most acute form in so-called pluripolar sexuality is due to the fact that fusion is taken as the criterion of sexual reproduction, and that factors associated with or determining it are designated sex factors. It is pointed out that this criterion has been derived by a double extension from the probably original criterion of sex, namely, differentiation into [male] and [female] individuals which developed in association with production and fusion of copulants, and of zygote nutrition, protection, and development. This first extension applied the terms [male] and [female] to the cellular products of the differentiated somas. Since fusion is the apparent function of these sex cells, and the nucleus came to be considered the essential element in the sex cells, caryog-amy and reduction have come to be considered the sex act, and the elementary criterion of sexual reproduction and of sex. From this derived position another extension was made in the contention that when cells or nuclei fuse to form a zygote, they are sex cells, and their producers, sexual individuals. The proposed clarification aims to avoid the difficulties of the sexual-asexual system of classifying reproduction and to create one of genetic significance. It is based on the course and type of nuclear behavior in the production of individuals. All reproductive processes are grouped into amitotic and mitotic. The latter group is divided into 2 subgroups, one characterized by nuclear change, and designated as caryallagic reproduction; the other, characterized by absence of nuclear change, and designated as acaryallagic reproduction. Caryallagic reproduction is subdivided into 7 categories on the basis of the time relationship of caryogamy and reduction division, or of caryozeuxis and caryogamy or dicaryolysis, and of irregularities during mitosis. Acaryallagic reproduction is subdivided into reproduction by cell division, and by budding and vegetative propagation. Sexual reproduction in this system is a special type of caryallagic reproduction characterized by sexual differentiation of the individuals or organs bearing copulants, or of the copulants themselves. The relative advantages of caryallagic and acaryallagic reproduction in changing and unchanging environments are pointed out and the occurrence of both of these types of reproduction is rationalized on the basis of their survival value to organisms.