Pavel Evgrafovich Sosin was born in St Petersburg in 1895 in the family of a petty office worker. He received his secondary education at the Agricultural School of Saratov oblast. After finishing school, he worked for 13 years as an agronomist in Odesa oblast, Ukraine, and then in Chistopol, Tatarstan, Russia, where he delivered lectures at both the Agricultural and the Teachers' Training Technical Schools. In 1921, he returned to Odesa and studied at the Odesa Agricultural Institute without interruption of work. From 1928 he worked as an agronomist-economist in Vinnitsia oblast, Ukraine and, in 1930, moved to Vinnitsia Teachers' Training Institute where he shortly took the chair. At that time Sosin published his first mycological papers. They were mostly popular in character: from 1936 to 1939 in the pages of Priroda [Nature] magazine were published articles about edible fungi and their storage, about some poisonous fungi of Vinnitsa oblast (Amanita phalloides, A. muscaria), and about Entoloma lividum and Panus tigrinus in Tsurupinsk forest of Kherson oblast, Ukraine. When the Biology Faculty of Vinnitsia Teachers' Training Institute moved to another town in 1935, Sosin moved to Kherson. There he lectured in the Agricultural & Teachers' Training Institute, holding the chair. In 1937, he defended his candidate degree on edible and poisonous fungi, and in 1938 moved to Poltava Teachers' Training Institute, where for more than 25 years he held the Chair of Botany and gave lectures until retiring on a pension. Among mycologists of the former Soviet Union, Sosin was regarded as an acknowledged expert on the Gasteromycetes. The first time P.E. Sosin showed interest in this group was during his work in Kherson. He had the opportunity to inspect some plant communities of Nikolaev oblast (of which at that time Kherson was a part) searching for larger basidiomycetes including gasteromycetes. In 1939, he published a work on these fungi. Among 16 species of larger basidiomycetes found in different localities of Kherson and Tsurupinsk districts of Nikolaev oblast, Sosin particularly noted Globaria bovista [Lycoperdon bovista], L. giganteum) and, new for Ukraine, Phallus imperialis [Hyphallus imperialis]. His scientific and educational activities were interrupted by the Great Patriotic War [Second World War]. From 1941 to 1944 he was in Stalingrad [now Volgograd] oblast, where he worked as a chief agronomist on one of the machine and tractor stations of Nikolaevsk district. Remarkably, his interest to Gasteromycetes was not however halted in those hard times: he collected Gasteromycetes on saline lands, saltmarshes, and virgin semi-deserts of Stalingrad oblast. Returning after evacuation, Sosin worked at the Chair of Botany of Poltava Teachers' Training Institute. At the same time he arranged his collections and continued to study gasteromycetes from different regions of Ukraine. Using material brought from Stalingrad, he described the new species Phellorinia stepnovskii P. Soss. (Podaxaceae) and reported, for the first time in the USSR, from virgin saline wormwood steppe, Calvatia craniforme (Lycoperdaceae) and several other rare and interesting gasteromycetes. He chose this group of fungi as the subject of his doctoral thesis "Gasteromycetes of the Ukrainian SSR", which was prepared at the V.L. Komarov Institute of Botany, Russian Academy of Sciences, Leningrad [St Petersburg] and defended in 1953. Working on his doctor's dissertation, Sosin described 8 species and one variety of gasteromycetes new for science, including Cyathus brazlaviensis P. Soss. (Nidulariaceae), Lycoperdon poltaviensis P. Soss. and Tulostoma chersonensis P. Soss. (Tulostomataceae). These descriptions were made using specimens collected by Sosin in different regions of Ukraine, but mainly in Poltava, Vinnitsia and Kherson oblasts. Analysis of the huge amount of herbarium material from personal collections and from other collections of the former Soviet Union allowed Sosin to make well-grounded observations about adaptive significance of some morphological characters of gasteromycetes. Analyzing the subterranean forms of gasteromycetes Sosin noted the modifications of morphological structures, as appearance of new characters fitted the requirements of new functions. Sosin suggested that an example of such modification of mycelium of subterranean forms could be rhizomorphs, which reach a considerable size in subterranean representatives of the families Hymenogastraceae, Nidulariaceae, Phallaceae and Sclerodermataceae. He considered the size reduction of fruitbodies in subterranean forms as an adaptive modification completely compatible with conditions inside the soil: greater density, larger specific weight. Smaller fruitbodies resulted in a smaller spore mass, and this, in his opinion, was also an adaptation to subterranean conditions: in soil spores do not spread large distances. The simple peridial structure, providing rapid spore release is also an adaptation to ground-level life. Ground-level gasteromycetes have, in addition to characters common for both ground-level and subterranean forms (such as rhizomorphs), a number of unique morphological adaptations: a large fruitbody or, if small, numerous generally clustered fruitbodies, an incrassate peridium (which in more complicated forms consists of a three-layered exoperidium and a one-layer endoperidium with different structures), spore dispersal by capillitium through well-formed foramena on a cone-shaped offshoot of the fruitbody, and the presence of a false stalk or receptacle (which promotes spore dispersal by raising the spore mass a little over the ground surface). He considered the dominance of ground-level fruitbodies, the formation of water-retaining sandy exteriors to rhizomorphs, the presence of an endoperidium soaked by a suberin-like substance or a jelly-like endoperidium protecting the spore mass from parching all as special adaptations of steppe, semi-desert and desert gasteromycetes. After defence of his doctoral thesis, Sosin as a chief expert on gasteromycetes continued processing his collections of fungi from different regions of the former Soviet Union, especially from the Russian Far East. As a result of this work, he described some species new for science including Abstoma fibulaceum P. Soss. (Lycoperdaceae) and Nidularia heterospora P. Soss. (Nidulariaceae). He also identified a number of species, which were collected for the first time in the former Soviet Union, mainly from different parts of the Russian Far East, including Calvatia lepidophora, Geastrum floriforme, Lycoperdon eximium, L. oblongisporum and Phallus rubicundus. Sosin summarized his data on species diversity, morphology and ecology of gasteromycetes of the former Soviet Union in his manuscript Guide to the Identification of Gasteromycetes of the USSR. The first version of the manuscript was ready in 1964 under the editorship of E.H. Parmasto. In 1966-1967 Sosin revised and work. As an editor of the second version, L.V. Vasil'eva worked very thoroughly on the manuscript. She and E.H. Parmasto became the editors responsible for the book, which appeared in 1973 in Leningrad [St Petersburg] after Sosin's death. Simultaneously with writing his Guide to the identification of gasteromycetes of the USSR, Sosin from the mid 1960s onwards prepared a part, devoted to gasteromycete orders for the key work Guide to the Identification of Fungi of Ukraine. The second book of the fifth volume of this edition, with its part on gasteromycetes written by Sosin, was published in 1979. Unfortunately, Sosin did not see these editions. He retired for health reasons and died in 1969. His collections of gasteromycetes were stored for some time in Poltava Regional Museum, then 721 packets were donated to the Nacional Herbarium of Ukraine (KW) at the M.G. Kholodny Institute of Botany, National Academy of Sciences of Ukraine, where they reside in the mycological reference collection. Lists. Publications. Kirk & Ansell form of name: Sosin.