INTRODUCTORY 13 



About 500 species of slime-moulds have been described. Saccardo 

 enumerates 443, inclusive of those denominated doubtful or less per- 

 fectly know^n. These 443 species are distributed among 47 genera, 

 of which 15 are represented by but a single species each, — mono- 

 typic. In the United States there have been recognized about 300 

 species. Of those here described, some are almost world-vv^ide in 

 their distribution, others are limited to comparatively narrow boun- 

 daries. 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 Cala- 

 magrostisj 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 sper- 

 nendi. 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.^ 

 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 un- 

 certain myxos, with their fascinating problems proffered still in 

 forms of unapproachable delicacy and beauty, not without inspiration. 



1 See Journal of Mycology, Washington, D. C, Vol. VII., No. 2 ; also 

 Bulletin No. 66, Agric. Station of Vermont. See also Bull. 33 Arizona Agric. 

 Ex. Station: An Inquiry into the Cause and Nature of Crown-Gall. J. W. 

 Tuomey. Also Bull. Torrey Bot. Club, Vol. 21, p. 26, where it appears that 

 club-root may attack crucifers generally. 



Professor B. M. Duggar in Fungous Diseases of Plants, pp. 97-102, gives 

 to club-root an illustrated chapter. 



