A SERIOUS LETTUCE DISEASE. 
137 
annual plant, which if not allowed to produce new seeds will eventually, 
upon the growth of all old seeds, be brought to the end of its existence. 
Sclerotia are not formed in diseased plants until the nutriment in 
the part affected is consumed, that is not until the plant has given 
clear easily discerned evidence of the presence of the parasite. If 
all such plants be pulled and burned no sclerotia will be made. The 
few small roots remaining in the ground will not usually be affected 
at this stage and even if they are, the formation of sclerotia in the 
roots under the ground is not common. This practice of constant re¬ 
moval of the sclerotinized plants will prevent the formation of new 
sclerotia and in course of time the sclerotia already present in the 
soil will have either decayed or germinated and thus become harm¬ 
less. As an additional precaution it is well to kill all mycelium which 
may be left in the locus of the removed plant by a liberal application 
of some disinfectant such as copper sulphate. It appears that this line 
of treatment is the most promising in cases where the destruction of the 
sclerotia by steam is not practicable. 
Since the ascospores are harmless except through the threshold of 
dead organic matter upon which to begin growth as saprophytes the 
careful removal from the bed of all torn, injured, sick or dead lettuce 
leaves should be practiced and manure and organic matter of other 
kinds had best be removed from the surface of the beds in the neigh¬ 
borhood of plants or covered so as to remove them from ascosporic 
infection. Similarly any injury to the plants as tearing the leaves, 
etc., which wrnuld result in dead bits of leaf, should be scrupulously 
guarded against. 
Since frequent stirring of the soil inhibits production of ascospores 
it will be well to rake over the top soil to a depth of a half-inch once 
each week. 
The above methods are of general application either in field or 
greenhouse. In addition to this soil disinfection, though it has not 
proved practicable in field or under canvas, is of great value under glass. 
Botrytis and Sclerotinia. 
Some species of Sclerotinia are genetically connected with Botrytis 
as a conidial form, notably: 
Sclerotinia fuckeliana has as conidial form Botrytis cinerea Pers. 
Sclerotinia vaccinii has as conidial form a Monilia. 
Sclerotinia cinerea Sch. has as conidial form Monilia cinerea Bon. 
These facts together with the sometime association or botryose and 
sclerotiniose upon the same plant very naturally led to the assump¬ 
tion that the Botrytis of the lettuce sustained genetic connection with 
Sclerotinia libertiana upon the lettuce. 
Conflicting views have been held upon this point. Thus DeBary 23 as 
early as 1886 held that Sclerotinia limertiana had no true conidial 
form while some other species of the genus did produce Botrytis 
conidia. Humphrey 5 of the Massachusetts Agricultural Experiment 
Station says that the rotting of lettuce is due to Botrytis vulgaris Fr. 
which “is with little doubt the conidial stage of some sclerotium pro- 
