THE BOOK OF THE PEONY 



Cause. — The cause of this disease has long 

 been attributed to the fungus, Botrytis, found 

 constantly associated with the lesions on stem, 

 bud, and leaf. There are many described species 

 of Botrj^tis, some of which are very common on 

 greenhouse and garden crops. The Botrytis 

 forms found on peony have been referred usually 

 to Botrytis vulgaris or Botrytis cinersa, and Bo- 

 trytis pceoniw, the last described by a Hollander 

 as the cause of the disease in that country. My 

 own studies indicate that there are a least two 

 distinct species of Botrytis atacking and causing 

 identical sjTiiptoms in the peonies both in this 

 country and in Europe. The species while quite 

 distinct in structure are very similar in their life 

 habits and effects on the peony. One forms large 

 sclerotia (resting bodies), while the other forms 

 very minute ones. I have never seen the sclerotia 

 of the large form except in my cultures, but the 

 small ones are conmionly formed in the diseased 

 stalks just beneath the epidermis and appear as 

 black pimples the size of a pin-head. Presumably 

 they serve to carry the fungus through the Winter 

 on the old stubble left by cutting away the tops. 

 There in the Spring they probably give rise to a 



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