LILY DISEASES. 



37B 



the parts attacked are either completely destroyed or so disfigured that 

 the plant is rendered worthless. 



When this disease appears, it usually assumes the dimensions of an 

 epidemic, attacking every plant in the vicinity, owing to the fact that the 

 fungus has become a true parasite in the sense of its mycelium being- 

 capable of penetrating the substance of the host-plant immediately on 

 germination, whereas in many kinds of Botrytis the mycelium first pro- 

 duced on the germination of the conidia, or reproductive bodies, requires 

 to obtain its food from dead organic matter, present in the soil or else- 

 where, for some time before it is capable of penetrating the tissue of a. 

 living plant. 



The rapid extension of the disease during the summer months is due 

 to the conidia formed on the delicate grey mould being conveyed by wind 

 or other agents from one plant to another, every conidium alighting on 

 the surface of a damp leaf or flower-bud being capable of producing a 

 diseased spot. 



In the meantime numerous conidia fall to the ground, where they 

 germinate and form a mycelirm, which obtains its food from organic 

 matter present in the soil. This mycelium continues to grow, and 

 eventually forms a cobweb-like weft, which often proves very destructive 

 to seedlings of various plants. When this mycelium develops in the soil 

 in greenhouses, &c., it continues to spread for years if the soil is not 

 entirely removed and the house thoioughly sterilised, never producing 

 fruit, and attacking almost indiscriminately all kinds of plants, especially 

 during the seedling stage. This destructive vegetative condition of 

 Botrytis cinerea is very well known in France under the name of la Toile^ 

 and is far more widely diffused in England than is generally supposed (2). 



The mycelium that forms in the ground in the open air remains 

 passive during the winter, and, on the return of spring, produces a crop 

 of conidia, some of which find their way on to the leaves or flowers of 

 Lilies. In some instances the mycelium in the ground attacks the scales 

 of Lily bulbs, where it forms numerous small, externally black, hard 

 bodies called sclerotia, which are more or less embedded in the flesh of 

 the scales. During the following season these sclerotia either directly or 

 indirectly give origin to conidia, some of which find their way on to the 

 foliage of Lilies. 



In Bermuda the cultivation of the 'Easter Lily ' — Lilium Harrisii — 

 is conducted on a large scale, mainly for the New York market, and since 

 1885 a disease, which has continued to spread annually and threatens to 

 extinguish the industry, has been shown by Kean (3) to be identical with 

 the Botrytis disease described above. In investigating this disease Kean 

 observed that certain Lilies sheltered from the heavy dew by growing 

 under Oleander hedges were not diseased. Literally interpreted, this 

 observation means that the conidia of the fungus cannot germinate and 

 enter the tissues of a leaf with a dry surface, and the hint given is 

 significant. Another pathologist, who has investigated the same subject 

 in Bermuda, attributes the disease to a variety of causes, but mainly to 

 the attacks of the bulb mite — Bhizoglyphus cchiiwps (4). My own 

 experience of this mite is that it is not a primary cause of disease, but 

 rather that it performs the functions of a scavenger, consuming diseased 



