THE FUNGI WHICH CAUSE PLANT DISEASE 



Mjrxogastrales (p. 5) 



This order comprises some forty-seveij genera and four iiun- 

 dred species of great variety and beauty. The plasmodium, 

 which varies from a millimeter or less 

 to several decimeters in diameter, pro- 

 duces either flat encrusted masses of ""^ '''^"^ 

 spores, aethalia, or develops spores in \ ^^J^ 



sporangia which show some superficial f^X-^'''' ^■'' 

 resemblance to very small puffballs, 

 Fig. 2. The interior of the sporan- ---iitJ 



gium is often permeated by a thread- ■^^°um;Tp<rre?c"aTc''ar°eous'c^- 

 like structure, the capillitium. They t'^'^- After Mac bride. 

 are not parasites but occasionally injure plants by overgrowing 

 them. 



Key to Families or Myxogastrales 



Spores not enclosed in a sporangium, borne 



externally upon the fruiting bodies. ... 1. Ceratiomyxaces. 

 Spores enclosed in a sporangium 



Capillitium wanting, or very poorly de- 

 v«loped 

 Periderm of uniform thickness, rup- 

 turing irregularly 2. Liceaces. 



Periderm of unequal thickness 



Periderm with a subapical thin line, 



opening by an operculum 3. Orcadellaceae. 



Periderm unequally thick above, the 

 thin portions evanescent, leaving 

 a network formed by the thicker 



portions 4. Cribrariacete. 



Capillitium well developed 

 Calcareous deposits absent, or rarely 

 present in the periderm 

 Capillitium of hollow, usually sculp- 

 tured threads; spores light colored 5. Trichiacese. 

 Capilhtium of solid, smooth and 

 usually much branched threads; 

 spores dark colored 

 Fruiting bodies sethalioid or in- 



