MYXOG AS! RALES 



149 



The organisms belonging to the class Myxomycetes * may be 

 separated into three orders as follows : 

 Saprophytic ; not uniting into definite plasmodia; no common sporangial 



wall. Acrasiales. 



Parasitic in living plant-cells, forming a true plasmodium. 



Plasmodiophorales. 



Saprophytic ; forming a true plasmodium from which spores are developed, 

 usually in sporangia. Myxogastrales. 



The first order contains a few little-known organisms that are 

 found mostly in manure ; the American forms have never been 

 specially studied. 



The Plasmodiophorales contain a series of parasites mostly at- 

 tacking the roots of various plants, producing root tubercles. 

 Frankia alni quite commonly produces root tubercles on Alnus, 

 and F. ccanothi is equally common on the roots of Ceanothus 

 Americanus. Plasmodiophora brassicae causes the so-called club- 

 foot f of cabbage, turnips and other plants of the mustard family, 

 both wild and cultivated ; it frequently causes considerable 

 damage. 



The true slime-moulds belong to the Myxogastrales. No two 

 writers agree on the division into families, genera, or species, but 

 the following artificial synopsis will probably be useful in enabling 

 a student to recognize the genera found in this country : 



1. Spores white, developed on the outside of the plasmodium. 



CERATIOMYXA. 



Spores developed within sporangia, plasmodiocarps or aethallia. 2. 



2. Spores brownish or brownish violet. 3. 

 Spores never violet tho usually bright colored. 20. 



3. Capillitium present among the spores. 4. 

 Capillitium wanting. PROTODERMIUM. 



4. Sporangia with deposits of lime on the outer surface. 5. 

 Sporangia without deposits of lime on the outer surface. 13. 



5- Sporangia simple. 6. 



Sporangia united in an aethallium. 12. 



* As stated on p. 19, it would seem best to regard the Mycetozoa as con- 

 stituting a phylum or primary division of the plant world. The phylum 

 then will contain the single class Myxomycetes. 



f This is not to be confused with similar swellings produced in the South 

 and elsewhere on many cultivated plants by nematode worms. 



