1892.] PUBLIC DOCUMENT — No. 33. 221 



surface with which it is in contact. These " organs of 

 attachment " have been observed by several students of 

 these fungi, but their real significance is not yet understood. 

 The compact mass is formed by the interweaving and grow- 

 ing together of numerous short branches of the filament .on 

 which the}' are formed. I have noticed, also, that an aT)un- 

 dant development of these organs is usually associated with 

 the formation of few conidia, and vice versa. But the con- 

 ditions which determine the preponderance of one or the 

 other are very uncertain ; for, in case of two parallel 

 cultures prepared in the same way and carried on under 

 apparently identical conditions, one produced abundant co- 

 nidia and few attachment organs, while in the other the 

 former W(tre few and tlie latter were very numerous. 



The history and structure of this fungus, as above de- 

 scribed, would lead to the expectation that there will be 

 found among the remains of the decaj'ed plants the small, 

 black masses of compacted threads known as sderotia, which 

 constitute the resting states of related fungi, and from 

 which, finally, the perfect fructification is developed under 

 favoring conditions. Careful examination of a quantity of 

 material has failed to show any of these bodies ; but it is by 

 no means certain that they may not be formed, at least in 

 some cases 



In its development, so far as observed, and in the details 

 of its structure, this fungus appears to agree with the form 

 known as Botnjtis {Pohjacfis) vulgaris Fr., and is with 

 little doubt the conidial stage of some sclerotium-producing 

 Peziza ( Sderotinia) . 



From what has been said, it is evident that the thorough 

 and careful culture and vigilant supervision of the plants are 

 essential to the control of the disease in question. The 

 nature of the crop forMds the trial of fungicides, and chief 

 attention must be devoted to the healthy growth of the 

 plants. The soil should be rich and mellow enough to in- 

 sure a rapid and vigorous growth. The temperature of the 

 houses should not be allowed to rise above the rather low 

 point which is most favorable to the growth of lettuce, since 

 a higher temperature diminishes the vigor of the plant and 

 at the same time favors the development of the fungus. Too 



