196 The Beneficial and Injurious Influences of Fungi. 



lingered for several years in some allotment gardens near 

 Selby, where year by year the potato is the staple crop but 

 is quite unknown to the farmers in the district where the 

 usual crop rotation is observed, although experiments at Kew 

 prove that the resting-spores in the soil are capable of imparting 

 the disease for five years. The spores are 40 X yofx diam. and 

 are not so easily carried by the wind as are those of Phytoph- 

 thora infestans, which measure only 25 X 15/j.. 



The Potato Disease (Phytophthora infestans), which causes 

 such enormous losses in favourable seasons, made its appearance 

 in this country in 1845, and is now known in every part of the 

 globe where the potato is grown. 



In dry weather, it does not assert itself, but when favoured 

 by moist warm weather the disease becomes of serious im- 

 portance. The usual mode of infection is through the leaves 

 by conidia brought by the wind. Each conidium contains 

 six or eight oospores which when liberated germinate at once 

 on the moist leaves and send out tubes penetrating the stomata 

 or boring through the cuticle, down the stems to the tubers, 

 which may either be destroyed at once or they may receive 

 the infection so lightly as to remain apparently sound until 

 the following spring ; these, when planted, produce the disease 

 in their offspring, ready to break out under favourable climatic 

 conditions to complete the life-cycle. 



The American plant-pathologists have much confidence in 

 the spraying of the plants with Bordeaux mixture ; (Copper 

 sulphate 5 lbs., Quicklime 5lbs., Water 50 gillons). They 

 claim that by spraying the disease is held in check, and also 

 that the fungicide invigorates the foliage. 



The principle fruit disease with us is the Apple Scab and 

 Canker ( Venturia inaqualis). The variety of fruit bearing 

 the disease is usually condemned instead of laying the blame 

 on the pest, and very little attention is paid to its eradication, 

 but in the South and West of England, Canada, the United 

 States and Australia, where pomaceous fruits are extensively 

 grown, every endeavour is made to cope with it by pruning 

 and spraying, which methods are in the main successful. 



Our timber trees bear parasites which, unlike the micros- 

 copic ones previously mentioned, are composed chiefly of 

 large agarics and polypores. The destruction of the wood is 

 caused by the mycelium permeating the tissues of the wood 

 like the dryrot fungus (Merulius lacrymans), or by sending 

 out cord-like strands between the wood and the bark, robbing 

 the host of its sustaining fluids and eventually causing 

 strangulation. 



The questions will naturally be raised : ' Has the biological 

 study of these organisms resulted in any economic success ? 

 The answer is Yes, decidedly. For instance : — 



Naturalist, 



