71 



the leaves from falling on the wet soil, and to allow of watering without 

 wetting the surface of the leaves; (3) the destruction of diseased plants, 

 to prevent the spread of the disease; (4) the use of cuttings from healthy 

 plants ; and (5) the application of a fungicide at intervals of a week or ten 

 days, the two best being a solution of copper sulphate (1 pound to i.z 

 gallons of water), and a solution of potassium sulphide (1 ounce to 1 

 gallon). 



2. Damping-off of Seedlings (Pythium debaryanum, Hesse). 



Damping-off is a very common disease both in greenhouses and gardens. 

 Many kinds of plants are subject to the attacks of this disease, of which 

 crueifers are perhaps the most susceptible. Cucumber, sunflower, mangel, 

 corn, clovers, millet and other grasses are also readily attacked. The 

 vegetative portion of the fungus, the mycelium, consists of delicate much- 

 branched threads which penetrate between the cells of the plant and destroy 

 them. The fungus attacks the seedling at the surface of the ground and 

 causes it to topple over. This, in its turn, will infect other seedlings with 

 which it may come in contact, so that under suitable conditions of abund- 

 ant moisture the disease spreads rapidly. Spores termed conidia are 

 formed singly on branches of mycelium which grow out into the moist soil 

 or air. These spores germinate immediately after their formation and 

 attack healthy plants. Another kind of spore is formed also, but it requires 

 a short period of rest before it breaks up into swimming spores, each cap- 

 able of moving about for a time in a film of moisture. On coming to rest 

 it geraiinates, sending out a tube which may enter a healthy plant. 



There is a third kind of spore, an oospore, formed by the fertilization 

 of an egg cell by a male cell, which has a thick wall and passes through a 

 long period of rest. It also produces swimming spores before germina- 

 tion takes place. 



Treatment. — As the conditions which favor the development and 

 spread of damping-off are abundant moisture and warmth, it should be 

 the aim of the plant grower to provide good drainage to avoid crowding 

 or close planting and over watering, and to allow the entrance of plenty of 

 sunshine and air. If these factors are attended to, there will be little 

 danger from the attacks of this fungus. 



3. The Drop of Lettuce (Sclerotinia Libertiana, Fckl). 



This disease is frequently very destructive to lettuce crops in green- 

 houses, and one most difficult to control. It is also the cause of much loss 

 in producing disease in cucumbers, rape, hemp and forced vegetables. The 



