280 



PLANT DISEASES 



of potato. The general principles are, however, quite 

 similar ; namely, that the spores which scatter the disease 

 fall on the leaves or other above-ground parts of the 

 plants, where they may cause infection ; then they 

 start to grow and are killed if the spray material is 

 already on the leaf. 



Damping-off of Seedlings Soil Treatment. The dis- 

 ease known as damping-off is very common all over 



the world. It affects 

 many kinds of plants 

 under a great many dif- 

 ferent conditions. It is 

 most common and se- 

 rious in greenhouses and 

 nurseries. Pansies and 

 many other greenhouse 

 plants are very com- 

 monly severely injured. 

 In nurseries seedlings of 

 conifers and other plants 

 are seriously affected. 

 The disease strikes the 

 seedlings just after they push up above the ground 

 and while they are still very tender. It blackens the 

 stem just at the surface of the soil, killing it and caus- 

 ing the seedling to tumble over and finally to wilt and 

 die. 



This disease is caused by a fungous plant which exists 

 for the most part in the soil where the spores live over 

 the winter. There are, however, a number of fungi 

 which have been known to cause this disease, so that 

 damping-off in any particular case may be due to one 

 or more of these fungi. They do not all have the same 



FIG. 145. Flax Wilt. Wilted Seedlings. 

 (After Bolley.) 



