420 PLANTS AND MAN 



asexual spore bearing stalk which produces the spores that will 

 give rise to new plant bodies. In some of the Phycomycetes, 

 sexual reproduction is not dependent upon the existence of two 

 different strains of the fungus, rather both male and female 

 gametes are produced, side by side, upon the same plant. 



The bread mold discussed above is most common as a sapro- 

 phyte living upon bread, cake, and even leather, but under 

 certain conditions it may become parasitic, causing serious 

 damage to stored vegetables and fruits, and even to young 

 growing seedling plants. Before 1920 this organism destroyed 

 20-30% of the sweet potato crop each year by causing an injury 

 known as soft rot. Through the development of improved storage 

 conditions, and care in digging and transporting of sweet pota- 

 toes, the loss has been reduced to 5-10%. Strawberries are 

 likewise seriously injured by bread mold, shipments from the 

 south sometimes being almost a total loss due to the "leak" 

 caused by this organism. Since entrance to the fruit is gained 

 only through breaks in the skins, care in picking and handling 

 is essential, as well as storage in a cool, dry atmosphere. Other 

 fruits and vegetables which may be severely damaged by rots 

 due to bread mold include the Irish potato, peaches, pears, 

 quinces, cherries, plums, and peas. Entire seedlings, and the 

 leaves of mature plants, may be damaged by bread mold if 

 moisture conditions are favorable, which occurs especially when 

 plants are crowded in seed beds, and on greenhouse benches. 



The most serious disease of seedlings is the one known as 

 DAMPiNG-OFF, causcd by several different pathogens which 

 ordinarily live as saprophytes in the soil. In crowded propagat- 

 ing benches and seed beds, especially in greenhouses, hot beds, 

 and nursery seed beds of forest tree species, these organisms may 

 wipe out almost the entire stand of seedlings, necessitating 

 replanting. The fungus attacks at the soil line, girdling the 

 young plant stems and causing them to fall over. If the fungi 

 are abundant in the soil, many of the young seedlings may be 

 attacked and killed before they emerge above the soil surface. 

 In greenhouses and nurseries, control of damping-off is effected 

 by sterilization of the soil used in seed beds, either by the use 

 of heat, or by sprinkling with dilute solutions of fungicidal 



