312 



SCIENTIFIC AGRICULTURE. 



May, 1922 



are demonstrating the value of sulphur as 

 a medium for soil treatment. Martin in 

 1921 found that only 8.9 p.e. of clean tub- 

 ers developed in infested, untreated soil 

 but when 600 lbs. per acre of finely ground 

 sulphur were applied there were 33.5 p.c. 

 clean tubers and when 600 lbs. of inoculat- 

 ed sulphur were used per acre the clean 

 tubers reached 50.9 per cent. This, it is 

 to be remembered, is in soil severely in- 

 fested with Actimomyces scabies. In some 

 soils 600' lbs. of sulphur per acre might 

 be disadvantageous while 300 lbs. would 

 be satisfactory. .By inoculated sulphur is 

 meant sulphur having mixed with it soil 

 containing sulphur oxidising bacteria. 



(d) Skin spot, {Oospora ywstulans). 

 Reference has already been made to the 



fact that skin-spot has been shown by 

 Shapovalov to be a stage of Powdery 

 scab. (See Sci. Agric, 2 : 202, 1922.) 



(e) Silver scurf. 



Harz in 1871 first described this disease 

 ■when it occurred in Austria and since 

 then it has been found in Germany, Great 

 Britain, Ireland and North America. It is 

 caused by a fungus named Spondyloc- 

 ladum atrovirens Harz. 



Syniptoms 



In its early stages silver scurf, under 

 moist conditions, causes olive black patches 

 to appear on the surface of the potato. 

 These dingy patches are the conidiophores 

 and spores' of the fungus. The spots may 

 be small, or may cover an area half- an 

 inch or more in diameter. Later in the 

 season the surface layers are slightly 

 raised by the abundant growth of mycel- 

 ium in the cells below and at this time 

 small, black, superficial sclerotia are 

 formed. When washed the raised areas 



appear whitish or silvery, giving rise to 

 the name "Silver scurf". Still later in 

 the season these raised areas gradually 

 become depressed owing to the death and 

 collapse of infteted cells. If the season is 

 moist enough for rapid fungus growth 

 the areas, increase in extent until in 

 severe infectious the whole surface of the 

 tuber is involved and the fungus pene- 

 trates more deeply into the tissues. As 

 a result it is not unusual to find tubers 

 which are entirely discolored and shrunk- 

 en. Surface layers with sclerotia slough 

 off and thus infect the soil. 



Life History. 



The fungus overwinters as sclerotia 

 which are very minute. These may be 

 on the surface of the potato or in the cells 

 of the outer layers or in debris sloughed 

 off into the soil. How long such sclero- 

 tia may live in a dormant condition is 

 doubtful but given moist, warm environ- 

 ment and they germinate readily by coni- 

 diophores. Vegetative development is 

 rapid and from spore to spore occupies 

 a period of only four or five days under 

 optimum conditions. The conidiophores 

 are erect, dark-brown, and tall (120 mic- 

 rons) and the spores are borne in whorls 

 on the upper parts of the conidiophores. 

 The spores are dark brown, five to seven 

 celled and apparently quite resistant to 

 adverse conditions. It is thus possible 

 that spores developed later in the season 

 may over winter. 



Control. 



The ordinary methods of seed-tuber dis- 

 infection do not control this disease and 

 the only suggestion at present efficacious 

 is that of tuber selection. 



Books Reviews 



Farm Management, by R .L. Adams, 

 (McGraw-Hill Book Co., New York, 

 $4.00.) 

 "Farming is business. It is as much 

 business as importing goods, selling mer- 

 chandise, building ships, running a rail- 

 road, and handling a mine. Jointly with 

 industry in general, farming is subject to 

 business principles and reacts to economic 

 influences. The present day farmer should 

 recognise <^hat as such he is also essentially 

 a business man or else he must eventually 

 succumb in competition with otlier business 

 men." 



The above paragraph opens the first 

 chapter of this new volume on the subject 

 of farm management. Throughout tlie en- 

 tire discussion of the principles and details 

 involved m the successful operation of farm 

 lands, tlie importance of applying business 

 methods is continually emphasized. The 

 value of a training in the science of agri- 

 culture is not overlooked, but the futility of 

 attempting to farm commercially with no 

 other training than a scientific one is made 

 quite obvious. The combination of scien- 

 tific knowledge and business acumen is ne- 

 cessarv if success is to be achieved. 



