G. MASSEE — PARASITIC FUNGI. 15 



The ohanjic in a funij-xis, howovor, is flifPercnt from that in an 

 individual who varies his pursuits. Such an individual docs not 

 gi'ow two pairs of legs or arms as he needs them, while a fungus 

 will, in its own province, do such a thing ; but a simple parasitic 

 fungus can only do one thing at a time, not having the advantage 

 of the division of labour which we possess. 



Coming now to our special subject, plant-diseases caused by 

 fungi, there ai'e some whose general aspect would have been recog- 

 nized at once by the aid of the lantern from the representations 

 of them which I have brought with me, but failing that I will 

 represent their characteristic features on the black-board. 



One of the broadest rules which can be laid down with respect 

 to fungoid diseases is that all fungi are favoured in their develop- 

 ment by the presence of acids, while alkalies are detrimental to 

 them. On the other hand, the group of allied organisms — the 

 Bacteria, which are popularly known as "germs" — do not thrive 

 under the action of acids. Farmers have said that the intro- 

 duction of artificial manures has brought nearly all the common 

 plant-diseases which are due to fungi, and from their standpoint 

 this is practically the case ; but the scientific explanation is that 

 these manures, or most of them, are prepared from raw, crude 

 acids, and the acids which are present in all the rich modern 

 manures, such as bone-manure and superphosphate, favour the 

 development of the fungi which do so much injury. They do not, 

 of course, create the fungi ; they merely favour their development 

 in the soil, giving them an advantage in their struggle to hold 

 their own against hundreds of other organisms. 



One of the most familiar instances of diseases caused by fungi 

 is that known as " finger-and-toe." It was known long before 

 it became so common as it is now, but it was only known that it 

 was something wrong with the root of a cabbage or of a turnip. 

 The lumps and swellings on the roots of these and other plants, 

 called " finger-and-toe" disease, have now been traced to a minute 

 organism belonging to the Mycetozoa, called Plasmodiophora 

 hrassica. This minute organism has done injury to the extent 

 of thousands of pounds to the farmers in England, but it is one of 

 those things which can easily be got rid of. A few drops of 

 ammonia in a bucketful of water, if applied to the roots of the 

 plant attacked, will prevent its growth, and lime in a soluble 

 condition will kill the spores. If quicklime be spread over the 

 soil, such a solution will be formed when rain falls. Potash, 

 however, is better than lime, because, when in solution, it is the 

 best manure for plants, and without it turnips cannot have their 

 best feeding properties, although it is possible to grow one species 

 of turnip when potash is not present. This fungus grows rapidly 

 in the soil at the present day owing to the amount of acid that is 

 supplied by so-called artificial manures, and that is the reason why 

 farmers say that with the introduction of these manures " finger- 

 and-toe " disease became rampant. 



Hertfordshire is a rose-growing county, and probably all the 



