158 PLANT DISEASES 



The white mould is a Botrytis^ producing myriads of 

 conidia, which, carried by wind, inoculate other plants in 

 the vicinity. The sclerotia remain in the soil until the 

 following season, when they produce conidia which inocu- 

 late the stem near the ground. 



Preventive Means. — Drooping stems should be re- 

 moved at once to prevent the continued formation of 

 conidia and sclerotia. Gardeners have observed that the 

 application of green manure as a top-dressing causes 

 paeonies and other plants to become diseased, and this is 

 undoubtedly true. The manure, even if it does not contain 

 spores, affords a congenial matrix for spores and sclerotia 

 present in the ground, in which they reproduce themselves 

 rapidly, and in the spring, when the young stems push 

 through the manure, inoculation is almost certain to take 

 place. 



Where the disease has previously existed, the surface 

 soil should be removed, and replaced with soil mixed with 

 lime. 



Massee, Gard. Chron.^ Aug. 13, 1898, fig. 32. 



TULIP MOULD 



{Sclerotmia parasitica^ Massee. 

 ^Botrytis parasitica^ Cavara.) 



Cultivated tulips are often killed by a mould which 

 forms olive-brown, minutely velvety patches on the stem, 

 leaves, and flowers. At a later stage smooth lentil-shaped 

 sclerotia, at first grey, then black, appear, mostly in the 

 outer parts of the bulb, sometimes being so numerous as 

 to form black crusts. 



