290 SUMMARY OF CURRENT RESEARCHES RELATING TO 



was found in many districts. In Iowa 50 to GO p.c. of the plants were 

 infected, and occasionally a whole crop is destroyed. In other districts 

 the disease was equally destructive. The varieties of sweet potato that 

 are immune were noted. 



Black rot is caused by Sphaeronema Jimbriatum. It has a wide 

 distribution, and in some localities is more serious than the stem rot. 



Foot rot has also spread to new localities, and causes much damage. 

 It is a comparatively new disease caused by Plenodomus destruens. At 

 Sikeston, Missouri, individual plants were found in which the organism 

 had grown down from the stem into the roots, forming fruiting bodies 

 and partially decaying the tissue. A pure culture of Plenodomus was 

 obtained from the decayed tissue within the potato. 



Silver-leaf Disease.* — J. M. Hector has carried out an investigation 

 on this disease, which is very prevalent in Berkshire, Hampshire and 

 Middlesex. In the latter county 10 p.c. of the plum trees were attacked. 

 The disease was also observed on greengage, damson, peach, nectarine, 

 gooseberry, red currant, cherry, cherry-laurel, lilac and elder. 



There is every reason to believe that the disease is usually spread by 

 air-borne spores, and grafted trees are frequently attacked through the 

 wood exposed by the grafting process. 



Silver-leaf is a wound parasite. All dead wood should be removed 

 and burned before the fructifications of the fungus causing the disease 

 have time to develop. 



Treatment of Potato Wart Disease.! — Experiments on badly 

 diseased land have been made at Bardon Hill, near Leicester, by treating 

 the soil with various substances. Watering with a solution of commer- 

 cial formaldehyde was ineffective ; the only potato not attacked being a 

 well-known resistant type. 



Other experiments in Lancashire with formaldehyde, mercuric 

 chloride and sulphate of potash also failed to achieve satisfactory results. 

 Mercuric chloride seemed to have increased the amount of disease. 

 Formaldehyde made no difference. 



Near Sutton Coldfield laud was treated with superphosphate, and 

 with superphosphate and soot in equal proportions, with copper sulphate 

 and with kainit ; still another plot was treated with salt. The test was 

 not absolutely satisfactory owing to unfavourable weather conditions, 

 but on the whole the results showed that in no case was there freedom 

 from disease. The crop was very poor where salt was used. 



* Univ. Coll. Reading, Faculty of Agric. and Hort., Bulls. Nos. 23-4. See also 

 Journ. Board Agric, xxi. (1915) p. 1141. 



t Journ. Board Agric, xxi. (1915) pp. 1126-8. 



