70 



young- tuber, gives rise to others and ultimately to a plasmodium. As in 

 the case of Club-Root, cells so infected divide more rapidly than healthy 

 cells, and a mass of tissue is formed which projects as a scab or pustule 

 but "which is covered bv the unbroken skin of the tuber. Each cell of this 

 tissue contains a plasmodium which finally changtes into a mass of spores, 

 a change followed by the collapse of the host cells so that the pustule 

 becomes filled \vith the loose spore-balls forming the powder previously 

 mentioned. It will be seen that the life-history closelv resembles that 

 of the Club-root organisms, the chief difference being that in the latter 

 myriads of separate spores are formed, while in the former all the spores 

 from one plasmodium adhere together as an irregular rounded mass, — 

 the spore-ball. 



Control. No effective control measures are known, and since the 

 disease is capable of proving verv serious it is desirable to take all possi- 

 ble precautions against its introduction into uncontaminated land. To 

 this end it is best if possible to procure "seed" onl}- from localities w^here 

 the disease is kno^vn not to be present. As this ho^vever is not always 

 possible "seed" potatoes should be selected which are quite sound and 

 then treated! \vith formalin or corrosive sublimate in the way comm.on- 

 ly practised for common Scab. The reason for this is that perfectly 

 sound tubers from a crop which contained diseased ones may have many 

 spore balls adhering to them w^hich \vould introduce the disease into the 

 soil. Similar treatment of tubers which actually have the disease even 

 in a mild form \vill not render them safe to use for planting as it seems 

 probable that the parasite mav exist to some extent in the living cells 

 near the scabs and not be reached bv the treatment. 



In order to restrict as far as possible the spread of the disease w^hen 

 it is knoxvn to exist on a farm it is important that special care should be 

 taken in the disposal of diseased potatoes, peelings etc. Moderately at- 

 tacked tubers may be used for table purposes but the peelings should not 

 be thrown on the manure pile or fed to animals ^vithout being boiled. 

 In the same \^^ay all tubers fed to animals should be boiled first as the 

 spores may resist the digestive juices and pass out into the manure with 

 unimpaired vitalitv. The manure in sUch a case will be an effective means 

 of spreading the disease. Cellars, etc., where affected potatoes have 

 been stored, should be washed dow^n ^vith a strong solution of formalin, 

 and bags, baskets, etc., should be dipped in a similar solution. The spores 

 mav retain their vitalitv in the soil for an undetermined length of time, 

 and although no other crops are kno"^vn to suffer from the same disease, 

 yet in order to reduce the possibilitv of conveying spores to other fields 

 on implements, etc., it is advisable "^vhen not involving too great a loss 

 to put the infected areas to grass, clover, or alfalfa. 



MUCIIvAGO SPONGIOvSA (LKYS) Morg. SPUMARIA Alba (Bull). 



D. C. 



This is one of the commonest and most conspicuous slime-moulds. The 

 Plasmodium forms large dull-whitish masses spreading over dead leaves 



