General Diseases 21 



From its original points of attack it may spread rapidly to 

 adjacent plants, often sweeping the whole seed bed. 



Since the growth of these fungi is favored by moisture 

 and warmth, the trouble may often be checked or pre- 

 vented by keeping the beds cool and withholding any excess 

 of water; also by means of adequate ventilation, preventing 

 the accumulation of a vapor-laden atmosphere around the 

 bases of the plants. Thick sowing should be avoided. 

 Frequent stirring of the top soil around the plants aids in 

 drying it and may stop an incipient attack of damping-off. 

 Organic matter in the soil favors the growth of damping- 

 off fungi, and should be avoided. Fresh, clean sand is best 

 for most purposes of the seed bed and cutting bench. 



Soil known once to have sustained damping-off may be 

 regarded as infested with the fungus which caused it. Such 

 soils should not be used for seedlings or cuttings wit! i)ut 

 disinfection. If disinfection is impracticabL, the soil should 

 be removed, the containers thoroughly cleansed with a 

 spray of Bordeaux, bluestone, or formalin, and new unin- 

 fested soil introduced or, in the case of seed beds, a new site 

 selected. 



Stem-rot, Root-rot ^^' ^^ {Corticium vaguvi B. & C, Rhizoc- 

 tonia). — The affected plants are usually attacked near the 

 soil-line or on the roots where cankers of small or large extent 

 develop. These cankers vary in character and color with the 

 host and conditions so that reliable diagnosis can be made 

 only by recognition of the fungus with a compound micro- 

 scope. There appear very fine, cobwebby threads, pale or 

 (|ark, which are often barely visible around the roots of the 

 affected plants as they are pulled from the ground. Masses 

 of fungus threads (sclerotia), also often occur. These are 

 black, irregular in shape, the size of a pin-head or larger. 

 Usually the fungus does not bear spores, but in relatively 

 rare instances sporiferous regions develop encircling the 

 stem. 



This stem-rot has long been known in Europe, and is now 

 found in North and South America, the West Indies, India, 



