834 EXPERIMENTAL FARMS 



5 GEORGE v.. A. 1915 



rofcived from farmers or fruit-growers, lliich time would be saved if more care were 

 taken in packing tlie specimens so that they would arrive in better condition. The 

 (.•ondition of some specimens is so bad that no result can be gained from an examina- 

 tion. Samples of diseased roots should be free from soil, which should be shaken but 

 not washed off. Leaves and like specimens might be wrapped with rhubarb or cabbage 

 'leaves, when they will arrive in a fresh condition. It is of no use to send putrid matter 

 — no advice can be given on specimens not in a fit condition for examination. The 

 sending of good specimens showing the disease and its progress from the earliest stages 

 to the more advanced is particularly requested. In the ease of bacterial troubles, which 

 spread very rapidly, this attention is most important. 



DISEASKS FURTHER STUDIED OR RECKXTLY OBSERVED. 



Potato Diseases. 



Powdery Scab. — Jveference has already been made to Powdery Scab, on the sub- 

 ject of which Circular l^o. 5, prepared by Mr. J. W. Eastham, has- been published. 

 Common Scab. — A study of the organism of Common Scab has been commenced, 

 which led to various new phases of research. The organism hitherto referred to as 

 Oospora scabies Thaxter was originally, but provisionally, described by Prof. Roland 

 Thaxter. After isolating the organism from tubers grown on the Central Farm, it 

 was carefully studied, when it was found that it properly belongs to a group of 

 bacteria known as sheath bacteria (Chlamydobacteriaceae), viz., Actinomyces. This 

 genus commonly occurs in the soil and it will be found most important to carefully 

 study these organisms with a view to the determination of their parasitism towards 

 plants and animals. One species (A. bovis) causes the well-known " lump jaw" in cattle. 

 We have also observed one species that occurred in milk. The disease "Acti- 

 nomycosis " is known to have been found in the udder of cows, and the causal organ- 

 ism may then be found in milk of diseased cows. This germ also occurs in the air, 

 water, on hay, and pasture herbage. Prof. F. Lafar in his " Handbuch " points out 

 that frequently serious cases of disease have been observed, which apparently origin- 

 ated from the use of straws and grass haulms as "toothpicks" — by no means an 

 uncommon peculiarity of persons walking through a field — which practice has resulted 

 in the development of "Actinomycosis" a disease painful at any rate, if not fatal, 

 which it may be once it reaches the lungs or respiratory organs. It is a fact which 

 we have often observed that Actinomyces may be isolated from herbage, particularly 

 of the order of grasses. The researches into the nature and relationship of the&e 

 organisms now being conducted in this laboratory may reveal interesting facts. 



Silver Scurf (See plate). — Of the potatoes sent in for examination from several 

 provinces during the past winter quite a large number were affected with this disease. 

 It is confined to the skin of the potato tuber and makes its appearance as ashy-grey 

 spots on the surface. These become larger as time goes on,- and several spots may 

 become confluent, thus covering a large area of the tuber. The outer layers of the skin 

 are killed by the fungus and take on a different colour from the healthy skin. Owing 

 to the silvery sheen of the dead skin, and to the fact that it dries up and peels off 

 readily, the disease has been given the appropriate name ai "Silver Scurf." In many 

 cases there is present, in addition, on the surface of these silvery spots, small black 

 specks which are just visible to the naked eye. These are the " sclerotia " of the 

 fungus, that is, each consists of a dense mass of closely interwoven fungus filaments, 

 and by means of these the disease is reproduced. 



If a tuber affected with Silver Scurf be washed and kept fairly moist for a few 

 (lays the surface of the silvered spot appears as though a very thin layer of soot were 

 (lusted over it. This dark powder on examination under the microscope is seen to 

 consist of the spores of the fundus. The funsal filaments running through the skin 



Ottawa. 



