730 JOL'ENAL OF THE KOYAL HORTICULTURAL SOCIETY. 



III. — Some Fungus Diseases of Herbaceous Plants. 



The fungus diseases of herbaceous plants are many, hence but few of 

 the most important can be dealt vrith. in the course of an hour's talk. 



Various kinds of the mould known as Botrytis, or possibly one kind 

 only, capable of assuming different appearances on different host-plants, 

 first claims attention. This pest has already been dealt with in the 

 Journal of this Society (xxvi. 41, 1901) as affecting Snowdrops ; but in 

 addition to this one host, practically every herbaceous plant, also many 

 woody plants, are attacked. To the naked eye this mould appears as a 

 dense olive-brown velvety nap, and when examined under a magnifying- 

 glass, such as all gardeners should carry, the heads of crowded spores can 

 be easily seen. 



There are at least two reasons why this fungus is so generally distri- 

 buted, being practically everywhere, and being capable of attacking 

 almost every kind of plant. (1) It can grow with equal vigour on decay- 

 ing vegetable matter or on living plants, consequently, wherever the 

 myriads of s^^ores happen to alight, they are almost certain to find some 

 substance upon which they can grow. Those rubbish-heaps consisting of 

 plants in all stages of decay, that are too frequently met with, even in 

 what are considered as well-kept gardens, are simply a paradise for our 

 Botrytis, where it can luxuriate in profusion and produce a sufficient 

 number of spores to infect all the plants growing in the neighbourhood. 

 (2) The germ- tubes, or first threads produced by the germinating spores, 

 contain an enzyme, or ferment, capable of dissolving the cell-walls of 

 living plants, thus enabling the mycelium to gain an entrance into the 

 tissues of its victim. 



In addition to spores, Botrytis possesses a second method of repro- 

 duction. After the fungus has reached the stage of forming spores its 

 mycelium forms numerous small solid lumps, at first white, finally 

 blackish externally. These bodies, called sclerotia, are more or less 

 imbedded in the dying or dead tissues of the host-plant. If a few of 

 these sclerotia are placed in sand and kept moist, after some months of 

 rest the surface of each sclerotium will become covered with a dense felt 

 of Botrytis mould, producing myriads of spores. In nature these 

 sclerotia lie on the ground when the plant on which they were formed 

 decays, and on the return of spring give origin to a crop of spores. 

 Every now and again a whole row of Scarlet-runners, or a plot of Broad 

 Beans, Potatos, or other cultivated plants, show indications of something 

 going wrong ; the leaves turn yellow, the stems droop, and finally die at 

 an early period, and the crop is a failure. If such plants are carefully 

 examined when the leaves are becoming yellow, tufts of Botrytis mould 

 will be found on the stem, near the base more especially. It is too late, 

 even now, to save the crop. If dead stems of the same are split open, 

 numerous black sclerotia, varying in size up to two lines long, will be 

 found imbedded in the central substance of the dead stem. 



Through lack of knowledge, the gardener would probably consider 

 the occurrence of such a disease as a mystery that could not be 

 accounted for. 



In the event of such an epidemic, probably one of the following two 



