622 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



in every case for green-fly. As might be expected, tlie delicate plants 

 required weaker solutions, and subsequent spraying with clean water 

 mitigated the action. 



Soft Soa/p and Tobacco, in the proportion of a pound and a half- 

 pound, respectively, to a gallon of water, was a good remedy for mealy 

 bug and green-fly on the plants mentioned. A little turpentine and the 

 addition of a pound of sulphur improved the wash for the Euonymus 

 and Solanum, but the Cinerarias were badly "burnt." A succession 

 of dilutions showed the caustic action not to decrease until the strength 

 of the constituents was reduced by one-fourth. A proprietary prepara- 

 tion, consisting mostly of soft soap and tobacco, also proved excellent 

 for mealy bug and aphides. 



Formaldehyde. — Series of experiments were tried with different 

 strengths of formaldehyde, alone and in combination with other sub- 

 stances. The solutions were made with Schering's formalin, the active 

 principle of which is formaldehyde, stated to be present in the pro- 

 portion of 40 per cent. Commercial formalin may be safely taken to 

 contain a less amount (average 35 per cent.). Since formalin is one of 

 the strongest antiseptics and fungicides known, it might reasonably 

 be expected that it would have insecticidal properties also, particularly 

 as it gives off the acrid vapour of formaldehyde in air. To test these 

 effects on the plants mentioned, solutions varying in strength from 

 "01 per cent, to 2 per cent, were used.* It was observed that 

 the toxic effect ol formaldehyde above '5 per cent, was marked on 

 Ampelopsis, Streptocarpus, and Coleus. Choisya, Euonymus, and 

 Solanum were sprayed with a 2 per cent, solution without injury, and 

 were completely cleared of green-fly, which did not reappear for tlie 

 summer. 



The Ampelopsis Veitchii was infested with hordes of woodlice, 

 which had their nests about its roots. On pouring some 2 per cent, 

 formaldehyde on the earth near the roots, woodlice poured out in all 

 directions, and were speedily overcome by the fumes. A spray of 

 "5 per cent, strength killed those which took shelter under the leaves; 

 stronger solutions had a deleterious action on the young shoots and 

 leaves. Traps of apple boiled in mercuric chloride solution were placed 

 about the roots, but practically no woodlice were snared, showing that 

 they had migrated or had been killed. 



An attempt was made to lessen the action of the formaldehyde 

 by adding soft soap. Here one would expect the strength of the for- 

 malin to be reduced by the organic matter in the resin soap. A slight 

 turbidity was produced on mixing, but the chemical changes which 

 might have been involved were not investigated. A typical wash was 

 composed of '5 per cent, formaldehyde (1 gallon) and soft soap lb.). 

 This injured the herbaceous plants almost as much as the formalde- 



* All these percentages refer to percentages of formaldehyde. It is easy 

 to calculate the actual amount of formaldehyde present in formalin spray, as 

 2"5 parts of Schering's formalin in 100 parts of water give a strength of 

 1 per cent, formaldehyde. 



