INTRODUCTION 11 



The Plasmodium does not always proceed to fructification without 

 interruption. Under the influence of dryness, cold, lack of food- 

 materials and probably other unfavorable conditions it may become 

 transformed into a hard, horny resting stage, or sclerotium. Within 

 the sclerotium, the protoplasm is aggregated in masses containing a 

 number of nuclei. In such condition the plasmodium may remain 

 dormant for a considerable length of time, presumably over winter 

 in most species of temperate climates, and in some cases at least for 

 two or three years, resuming activity with the advent of favorable 

 conditions. 



The Myxomycetes are of no direct economic importance. The ex- 

 clusion of the Plasmodiophoraceas removes the only group of plant 

 parasites. From time to time certain species appear on economic 

 plants — Physarum gyrosum on sweet potato vines, Physarum cinereum 

 on strawberry plants and lawn grass — but while they may alarm the 

 proprietor, they do no harm and soon disappear. A recent study by 

 Thorn and Raper (1930) shows that myxamcebae and plasmodia are 

 constantly present in the upper layers of soil and in the decaying 

 vegetable debris at the surface, and these authors note that members 

 of this group should be considered in studying soil microorganisms. 

 Active as they are, their role should be investigated, but nothing defi- 

 nite can be said to be known of it at present. 



II. Collection and Care of Specimens 



On this subject a word may here be appropriate. Throughout the 

 world, specimens may be gathered at the proper season in almost any 

 locality. Beginning with the latter part of May or first of June, in the 

 northern United States, plasmodia are to be found everywhere on 

 piles of organic refuse: in the woods, especially about fallen rotting 

 logs, undisturbed piles of leaves, beds of moss, stumps, by the seeping 

 edge of melting snow on mountain sides, by sedgy drain or swamp, nor 

 less in the open field where piles of straw or herbaceous matter of any 

 sort sink in undisturbed decay. Within fifty years tree-planting in all 

 the prairie states has greatly extended the range of many more defi- 

 nitely woodland species, so that the species of Stemonitis, for instance, 

 are common in the groves on farms far into Nebraska and Dakota. In 

 any locality the plasmodia pass rapidly to fruit, but not infrequently a 

 Plasmodium in June will be succeeded in the same place by others of 

 the same species, until the cold of approaching winter checks all vital 

 phenomena. The process of fruiting should be watched as far as pos- 

 sible, and for the herbarium material, allowed to pass to perfection in 

 the field. 



