About 500 species of slime-moulds have been described. Saccardo enumerates 443, inclusive of those denominated doubtful or less perfectly known. These 443 species are distributed among 47 genera, of which 15 are represented by but a single species each,--monotypic. In the United States there have been recognized about 300 species. Of those here described, some are almost world-wide in their distribution, others are limited to comparatively narrow boundaries. The greater number occur in the temperate regions of the earth, although many are reported from the tropics, and some even from the arctic zone. Schroeter found _Physarum cinereum_ at North Cape. Our Iowa forms are much more numerous in the eastern, that is, the wooded regions of the state. _Physarum cinereum_ has however been taken on the untouched prairie, and on the western deserts, as also _Physarum contextum_ on the decaying stem of _Calamagrostis_, far from forest. As to the economic importance of our myxomycetes, there is no long chapter to write. Fries says: "Usu in vita communi parum admodum sese commendant, sed in oeconomia naturae certe non spernendi. Multa insectorum genera ex eorum sporidiis unica capiunt nutrimenta." However this may be, there is one species which has come to light since Fries's day which is the source of no inconsiderable mischief to the agriculturist. _Plasmodiophora brassicae_ occasions the disease known as "club-root" in cabbage, and has been often made the subject of discussion in our agricultural and botanical journals.[13] Aside from the injurious tendencies, possible or real, of the forms mentioned, I know not that all other slime-moulds of all the world, taken all together, affect in any slightest measure the hap or fortune of man or nation. And yet, if in the economic relations of things, man's intellectual life is to be considered, then surely come the uncertain myxos, with their fascinating problems proffered still in forms of unapproachable delicacy and beauty, not without inspiration. COLLECTION AND CARE OF SLIME-MOULD MATERIAL