10 THE FUNGI WHICH CAUSE PLANT DISEASE 



definite, walk poorly defined, 

 fraying out into a pseudo- 



capillitium 6. Reticulariacese. 



Sporangia definite, true capilli- 

 tium more or less prominent 7. Brefeldiacea. 

 Fruiting bodies separate sporangia 

 with columella and abundant 



capillitium 8. Stemonitaceae. 



Calcareous deposits present 

 Capillitium' not calcareous 



Capillitium simple 9. Didymiacese, p. 10. 



Capillitium more intricate 10. Spumariacese, p. 11. 



Fructification calcareous throughout 11. Physaiaces, p. 11. 



Didjmiiaceae 



Fructification of separate sporangia or plasmodiocarps, periderm 

 simple or double, the outer calcareous; columella present or ab- 

 sent; capillitial threads thin, colorless or violet, arising from the 

 base of the sporangium or passing from the columella to the peri- 

 derm, usually without calcareous deposits, which if present are 

 very small crystals; spores in mass black, spore walls violet. 



Kgt to Genera of Didymiaceae 



Calcareous deposits in the form of stellate crys- 

 tals, frosting the surface 1. Didymium, p. 10. 



Calcareous deposits not stellate. 

 Calcareous deposits forming a superficial crust 2. Diderma. 

 Calcareous depHjsits forming large superficial 

 scales 3. Lepidoderma. 



Didymium Schroter 



Sporangia distinct, stipitate, sessile or even plasmodiocarpous, 

 never aethalioid; the peridium thin, irregular in dehiscence, cov- 

 ered with a more or less dense coating of calcareous crystals; 

 columella more frequently present; capillitium of delicate threads, 

 simple or sparingly branched, extending from the columella to the 

 peridial wall. 



D. daedalium. B. & Br. is occasionally injurious to melons in 

 culture.'"' 



