igi2.] Summary of Agricultural Experiments. 1039 



soon fall over, as in the disease known as "damping off." In both 

 peas and asters the roots of diseased plants are shrivelled and 

 blackened. 



Infection appears to take place only from the soil, and the disease 

 is often spread by means of manure, on which material the fungus 

 nourishes and reproduces itself at a rapid rate. It is practically im- 

 possible to cure affected plants, but preventive measures can be taken, 

 and in the article directions are given for sterilising the soil by means 

 of dilute solutions of formalin. 



Varieties of Potatoes immune to Wart Disease.— A small experiment 

 was carried out last season at Abertillery in Monmouthshire on the 

 lines adopted by the Board in the experiments described in the February 

 number of the Journal, p. 915. A plot infected with Wart Disease of 

 potatoes was selected and-- planted with potatoes known to be suscep- 

 tible to the disease, as well as those believed to be immune. The 

 resistant varieties planted were Aberlady Early, Conquest, Golden 

 Wonder and Langworthy. These all proved immune, were white 

 when cooked, and, except Golden Wonder, were floury. The following 

 report was made on their quality : Aberlady Early, excellent, a very 

 satisfactory potato ; Conquest, excellent ; Langworthy, very good ; 

 Golden Wonder, fair, rather small. 



The potatoes of the other varieties tried were all badly affected with 

 the disease. 



A New InseGt Pest of Mangolds and Beet (Second Report on Economic 

 Biology, by W. E. Collinge, 1912). — During May, 191 1, larvae of 

 Cionus scrophularicE, Linn., were received on mangold and beet leaves, 

 to which they were doing considerable damage. Hitherto no account 

 of this insect attacking cultivated plants has been recorded, and it has 

 not been regarded as of any economic importance, except for the fact 

 that it feeds upon the knotted figwort (Scrophuloria nodosa, Linn.), 

 and to a certain extent keeps down that weed. 



Contact Insecticides (Michigan Agric. Coll., Tech. Bull. No. 11). — 

 The term "contact insecticide" is used as referring to those sub- 

 stances which kill through coming in contact with the outer surface 

 of the insect body in contradistinction to those which must be eaten to 

 be effective. Little work has been done to determine exactly how such 

 substances kill, but the belief commonly held is that they act by 

 plugging up the breathing pores, thus causing death by suffocation. 

 This was the first point tested in the experiments reported on in this 

 bulletin. It was found extremely difficult to kill many insects in a 

 reasonable time merely by depriving them of air, and it is concluded 

 that the certain and fairly rapid death caused by such materials as 

 kerosene and gasolene cannot be due to the stoppage of the tracheae 

 alone. It was also found that air saturated with the vapour of various 

 insecticides was nearly as effective as the liquids themselves. Further 

 tests showed that in the use of many insecticides, such as kerosene, 

 gasolene, creolin and pyrethrum, vapour penetrated the tissues and 

 caused death long before the liquid or powder itself had time to pene- 

 trate the chitin, or to cause suffocation by the plugging of the tracheae. 

 The evidence gathered seemed to show that the vapours after absorp- 

 tion in the insect body become mainly effective through some tendency 

 their presence exerts to prevent absorption of oxygen by the tissues. 



