the definition of species as advocated by Ernst Mayr, Theodosius Dobzhansky, and G. Ledyard Stebbins had very little meaning for plants. In 1978 Sussman and Raven advanced the idea that nonflying mammals, such as primates and marsupials, could have been significant pollinators but were outcompeted by nectar-feeding birds and bats. Any coevolved relationships between flowering plant species and non-flying mammal pollinators that persist at the present would appear to be "living fossils, which have a great deal to tell us about the evolution of both the mammals, including some of our antecedents, and of the flowering plants." Raven wrote a review of the plant population data as of 1979, and identified several themes that he felt had potential for future research, including the above theme of the species problem. He went on to assert that developmental biology would be more important in the future He advocated another theme, that being that funding should be provided for study on a few species rather than spread amongst many in order to solve population biology problems: In 1980 Raven continued discussing problems associated with defining species in plants. He discussed the widespread ability of plant species to hybridize, especially in perennial plants, and the historical observations of such back to 1717. He used as examples of perennial plants in the genera Epilobium, Scaevola, Bidens, and Ceanothus as examples of plants that appeared to use hybridization as a means to adapting to new environments. He stated "If the hybrids are particularly favored in specific ecological situations, asexual reproduction, polyploidy, or simply autogamy may favor the perpetuation of specific genotypes through a narrowing of the spectrum of genetic recombination characteristic of the population. No general conclusions about the most appropriate way to treat these populations taxonomically appear to be possible." In annual plants, using examples from Clarkia, he asserted that several species of Clarkia often occur sympatrically, yet hybrids are very rare in the wild," and that much of the sterility is due to chromosomal repatterning between species." In 1980 Raven and coauthors reviewed the literature concerning fungal symbiosis in vascular plants. They reviewed two kinds of fungal-plant associations: ectomycorrhizal and endomycorrhizal. They reported that endomycorrhizal fungi, which penetrate plant cells, are found in 80% of all vascular plants, including ferns, gymnosperms, and angiosperms, and are found in forests of high species richness. On the other hand, ectomycorrhizal fungi, which do not penetrate plant cells,