22 Letters on the Diseases of Flants. 



Remedies. 



1. Avoid seed from a crop that has shown wet rot. 



2. Buy seed only on a guarantee that it comes from a perfectly sound crop. 



3. Where laud has borne a diseased crop of potatoes, do not again imme- 

 diately use it for potatoes. Give it a rest, or put in some other crop. 



4. Land lower down than that suffering from wet rot and receiving drain- 

 age from the contaminated land will also sometimes develop the disease. 

 Avoid such land for potatoes, 



5. Destroy the worst affected potatoes by fire. Boil the remainder of the 

 diseased tubers for the pigs, poultry, or other stock. The apparently sound 

 portion may be used for the table. In fairness to other people such potatoes 

 should not be sold, except with a full statement as to the facts of the case. 



G. Disinfect all bags, bins, and other receptacles that have held wet-rotted 

 potatoes. Boil the bags and whitewash the bins. I believe the steamboats 

 plying along the coast and to Tasmania and New Zealand are responsible 

 to a considerable degree for the spread of this disease. The precautions 

 just mentioned are inexpensive, and might with advantage be more often 

 adopted by the steamship companies. 



7. Do not store diseased potatoes along with healthy ones. 



8. Pick over the stored potatoes from time to time. Throw out and destroy 

 the diseased ones. 



9. Induce as many of your neighbours as you can to adopt these precau- 

 tions. Their vigilance will benefit you. 



Potato Scab. 



This is a well-known disease of the potato, characterised by the scabby 

 appearance of the whole or part of the surface of the tubers. The same 



Fig. 23.— Pliotograpli of a scabby potato, 

 *i_' _ r natural size. The rouudish and 



•>■ ~ ^ ^ irregular-sliapedrouyli and corroded 



"^^ ^ spots are due to the attacks of tlie 



scali organism, and it is from these 

 seal IS that spores or other agents 

 responsible for spreading the disease 

 are derived. Tlie dcjitli to which 

 some of the si-il.liy sjnii^ rxtendis 

 well shown at tlic 1'iiiol ; lir illustra- 

 tion, where a duep i;ivity is shown 

 in i^roflle. By soaking the potatoes 

 in corrosive sublimate solution these 

 scabs are sufficiently penetrated by 

 the poison to be well disinfected, yet 

 the potato tissues themselves, being 

 comparatively impenetrable, are not 

 injured. 



disease is said to occur on beet-roots. It occurs in all sorts of land, but is 

 more prevalent in sandy soils and in soils containing much lime, and is said 

 to be more virulent in crops fertilized with manure containing much common 

 lime, or with wood ashes. The disease is confined largely to the tubers, 

 the appearance of which, when thoroughly diseased, is shown in the above 

 illustration. 



The cause of the disease is still in dispute, but there can be little doubt 

 that it is a minute vegetable organism. On the one hand it is claimed by 

 some who have investigated the disease with care — and their view has at 

 present the most supporters — that the cause is a fungus of low degree,* 

 and on the other hand by others who also seem to have been careful, that the 

 cause is a microbe. These latter do not deny the presence of the fungus 



* The Oospora scabies o£ Thaxter, 



