INTRODUCTORY 13 



I. Myxomycetes. 

 II. Diatomaccce. 



III. Schizophyta includes the Schizomycetes and Cyano- 

 THALLOPHYTA: \ 



phycecE. 



IV. Algce, excluding Diatoms and Cyanophycece. 



V. Fungi, exclusive of Myxomycetes and Schizomycetes. 



This arrangement commits us to no theory, and enables us 

 to study together those forms which by common consent are 

 naturally associated. 



About 400 species of Slime-moulds have been described. 

 Saccardo enumerates 443, inclusive of those denominated doubt- 

 ful or less perfectly known. These 443 species are distributed 

 among 47 genera, of which 1 5 are represented by but a single 

 species each, monotypic. In the United States there have been 

 recognized about 200 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 most numerous in the eastern ; that is, the wooded regions 

 of the state. I have, however, found Physarum cinereum on 

 the untouched prairie, and on the western deserts, as also 

 Physarum contextum on the decaying stems of Calamagrostis. 



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 ceconomia 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 agricul- 

 turist. Plasmodiophora brassier occasions the disease known 

 as the " club-root " in cabbage, and has recently been made the 

 subject of special discussion in the Journal of Mycology! 



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

 No. 66, Agric. Station of Vermont. 



