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 A HISTORY OF HERTFORDSHIRE didus which grows on living plants, Acrostalagmus cinnabarius which prefers decaying plants, and the pest, Peronospora infestans, which produces the well-known potato-disease. 7. HYPHOMYCETES Of the moulds the only species we have on record are Tubercularia eesculi and vu/garis, Epicoccum purpurascens, Monotospora spharocephala, Verticillium /ateritium, and Polyactis cinerea. The common moulds belong- ing to this order, which attack almost everything left in a damp state or put aside in damp weather, are too familiar to require mention here, but it may be stated that nearly all the species of every-day occurrence are unrecorded. 8. MYXOMYCETES OR MYCETOZOA The curious organisms usually known as the Mycetozoa are with difficulty assigned to a definite position in any lineal system of classifica- tion. This arises from certain peculiarities which they exhibit during the changes of form through which they pass in the series of metamor- phoses constituting their life-cycle. In certain stages they show affinities with several groups of plants, by which they are linked to the vegetable kingdom, while in other phases of their life-history they present equally marked alliances with the animal world. Hence they may be described as lying on the borderland of the two great divisions of animated nature, suggesting that both these kingdoms have had a common ancestry. So different are they in some respects from all other known forms of life, that it has recently been suggested by an eminent biologist that they should be raised to the rank of a separate kingdom. For convenience' sake they are usually classed with the Fungi, the German author Sachs grouping them with the Zygospora, although he admits that they differ from these in certain important points. Mode of occurrence and general appearance. The Mycetozoa are usually found upon decayed vegetation, such as leaf heaps in the recesses of damp woods and other shady situations ; and on fallen branches and rotten tree-roots, especially if overgrown with vegetation. In addition to such situations, recent researches, dating from 1897, in Hertfordshire and the adjoining counties, have shown that old straw- heaps, such as are usually found on outlying farms, are very prolific in these organisms. These accumulations of decaying vegetation have yielded in this district several previously undescribed species and note- worthy British records. These are the two new species, Pbysarum stra- minipes and Didymium Trocbus ; a new variety, Pbysarum didermoides, var. lividum ; the first European record of Fu/igo ellipsospora ; and the first British record of Badbamia ovispora. A brief description of the Mycetozoa in the fruiting-stage will be helpful to those who may wish to observe them in the field. A common form, Didymium diffbrme, which often occurs in heaps of leaves or straw, presents the appearance of minute spherical white beads on short stalks. 76