236 



SCIENTIFIC AGRICULTURE 



March, 1922. 



If the soil is wet or poorly drained and 

 the temperature high severe infection may 

 completely cut off the young shoots be- 

 fore they appear above ground and this in 

 some measure accounts for misses in the 

 field. Sometimes side branches may grow 

 up from below the lesion on dead haulms 

 (Fig. 12) but such branches are weak and 

 spindling, with yellowish leaves. Older 

 plants severely attacked just below ground 

 Avilt and die off rapidly. Slight attacks 

 will produce lesions on the stem tending to 

 girdle it and in this case the tops are more 

 or less dwarfed and yellowed. As the 

 fungus gradually encircles the stem and 

 penetrates the tissues water supply is cut 

 off increasingly so that there is a shorten- 

 ing of upper internodes and dwarfing of 

 leaves which gives rise to "rosette top." 

 At the same time the leaves may be slightly 

 wilted and yellowish to reddish green in 

 color and curled. This curling is easily 

 distinguished from the crisp condition in 

 true Leafroll. 



When the stem is attacked at the time 

 of early tuber formation so that ample food 

 is being elaborated the girdling of the stem 

 cuts off J;he translocation of food to the 

 stolons. This disturbance in direction of 

 translocation causes the development of 

 aerial tubers in the axils of leaves. I found 

 many such cases in France during the war 

 and in all eases where aerial tubers were 

 formed there was a closely matted weft of 

 mycelial growth around the stem for about 

 two and a half inches above ground level. 

 That the formation of aerial tubers is not 

 due to root injury but changed transloca- 

 tion of elaborated food can be shown by 

 cutting away carefully the developing sto- 

 lons around the base of the stem when 

 aerial tubers begin to develop. 



On the other hand, if root infection oc- 

 curs the metabolism of the plant as a Avhole 

 is affected, the plant is definitely dwarfed 



and the leaves cannot function to a normal 

 extent ^0 that the potato tubers formed, if 

 any, are small giving the condition known 

 as "little potato." 



Life History of the Organism. 



Usually the mycelium does not give rise 

 to the sporiferous stage but late in the 

 season forms the small compact blackish 

 sclerotia on the surface of the tubers. If 

 tlie sporiferous stage is developed it occurs 

 on the weft of mycelium around the base 

 of the stem just above ground. Here the 

 spores are borne on basidia, four spores, 

 measuring 6-8 by 9-14 microns, each on a 

 short sterigma for each basidium. They 

 germinate and cause new infections in the 

 field. The mycelium can grow through or 

 over the soil and in one case north of Ar- 

 ras, France, the writer found that the my- 

 celium grew during two months of a cool, 

 moist summer ten yards along a row from 

 the originally infected potato. Cultivation 

 lietween the rows prevented its lateral 

 spread. 



Control. 



Since Rhizoctonia prefers heavy, moist 

 soils, drainage and the avoidance of heavj^ 

 soils difficult to drain is important. If 

 the soil is heavily infected it is inadvis- 

 able to plant potatoes. With ' ordinary 

 soils seed tuber disinfection should be 

 practised. In this connection Howitt at 

 Guelph is doing some interesting work on 

 control by corrosive sublimate. His work 

 for 1920 shows that treating tubers with 

 sclerotia on them for 2 hours in corrosive 

 sublimate 1 in 500 gave perfect control, 

 while treatment for 2 hours in a solution 

 1 in 1,000 reduced disfigured tubers to 14 

 per cent. The experiments are still in 

 progress. 



Erratum. 

 In the last issue pp. 203, col. 1, line 40, 

 read "in 1909" instead of "in 1919."— 

 B. T. D. 



Book R 



Efficient Marketing for Agriculture, 



by Theodore Macklin. (Macmillan Publish- 

 incr Company, Toronto, $3.50.) 



The modern farmer, even of the pro- 

 crressive tvpe, is inclined to give too little 

 consideration to the economic prmciples 

 upon which the business of farming is 

 based In many instances the care given 

 to the problems of production is not cou- 



eviews 



pled with equal care in the distribution 

 and sale of farm products. Unsatisfactory 

 prices are attributed to poor market con- 

 ditions, falling demand, and many other 

 factors, when the real blame coufd often 

 be placed directly upon poor grading, im- 

 proper distribution, lack of adequate stor- 

 age facilities, etc. If the producers of 

 agricultural i)roducts — the farmers 



