A SNOWDEOP DISEASE. 



41 



A SNOWDEOP DISEASE. 



By Geo. Masses, F.L.S. 



The disease under consideration was first described by Berkeley and 

 Broome in 1873* under the name of Polyactis galanthina, and stated to 

 be very destructive to Snowdrops." At a later period it was again recorded 

 as a destructive parasite on Snowdrops by Worth. G. Smith, t who adds 

 that the disease of Tulips s>nd Hcvca are caused by the same fungus. The 

 disease of Snowdrops is still with us, and, as we consider, is due to the 

 presence of the old and well-known fungus called Botrytis cinerea by 

 Persoon, w^hich is stated by De Bary to be the conidial form of the Peziza- 

 like fungus now called Sclerotinia Fuckeliana. 



The young leaves and flowers of the Snowdrop are attacked by the 

 fungus just below the surface of the soil, and by the time they emerge 

 above ground are much distorted and covered with a dense brownish 

 mould. This development often occurs when the ground is covered with 

 snow. Leaves and flowers thus attacked soon fall to the ground and 

 decay, the bulb in many instances being also reduced to a soft pulp by 

 the mvcelium of the functus. 



If a Snowdrop leaf infested with the fungus is placed in a nutrient 

 solution, such as a decoction of dung or plum juice mixed with gelatine, its 

 surface and margin soon become studded with minute blackish grains. 

 These grains are concentrated masses of the mycelium of the fungus, 

 called sclerotia, which continue to increase in size for some time and 

 assume various shapes, often growing into each other and forming a 

 black continuous crust. At the same time the mycelium of the fungus 

 present in the leaf spreads into the nutrient medium and in turn forms 

 sclerotia, so that in course of time hundreds of these bodies are produced 

 by a single diseased leaf. After a time the formation of sclerotia ceases, 

 and no further change takes place until the following spring, when the 

 sclerotia produce a crop of conidia or give origin directly to mycelium, 

 depending on their relative position in the nutritive solution. 



Now the formation of sclerotia as described above is exactly what 

 takes place under natural conditions : the diseased Snowdrop leaves fall to 

 the ground, where they form sclerotia ; the mycelium present in the leaves 

 also spreads into the soil and there forms more sclerotia, which remain 

 unchanged until the following spring, when those sclerotia that happen 

 to lie on the surface produce a crop of conidia, which germinate at once 

 and form a copious weft of mycelium that spreads in the soil, obtaining 

 its food from the humus present, and finally attacks the young leaves of 

 the Snowdrop as they emerge from the ground. Those sclerotia that are 

 buried in the soil or attached to a bulb do not bear conidia, but give 

 origin directly to mycelium, which behaves as already described. 



Numerous experiments have proved that the lea^•es cannot be infected 

 by wind-borne conidia alighting on their surface ; when conidia are placed 



* Ann. Xut. Hist. 1873, p. 346, pi. viii. f. 8. f Card Chron. 188'), p. *27o, tig. 49» 



