202 SCIENCE AND FRUIT GROWING 



strongest solutions (2 per cent.), a mortality of only 10 per cent, 

 was ever reached. As has been already mentioned (p. 165), a 

 mixture of the two alkalis produced no better results than either 

 of them separately. Subsequent experiments showed that an 

 almost complete mortality of the eggs might be obtained by 

 increasing the strength of the soda up to 2' 5 to 3 per cent., but, 

 unfortunately, such a strength cannot be used without risk 

 of damage to the trees, and danger to the workmen (VI, 53 ; 

 VIII, 41). 



Although the effect of the 2 per cent, alkalis on the eggs is 

 so small, their inefficiency as insecticides is not so complete as 

 might be inferred, for they appear to glue the scales on to the 

 bark so effectually, that the egress of the insects after hatching 

 is prevented (see p. 207). This glueing down of the scales is 

 preceded by their being softened and loosened. A similar 

 action in the case of lime-Lulphur and re; in-soap washes has been 

 noticed in America in reference to the San Jose scale. 1 



The next point examined was whether the destructive action 

 of alkalis could be enhanced by the presence of small amounts 

 of paraffin, soap or treacle. With treacle (o'6 per cent, of the 

 liquid) no improvement was obtained : with soap (up to o'6 

 per cent.), and with weak paraffin emulsions (1*25 per cent, of 

 paraffin), there was some improvement, but the mortality did not 

 exceed 10 per cent., and, therefore, could not be regarded as 

 satisfactory. The effect of using methylated spirits, both by 

 itself, and as a substitute for the whole or part of the water in 

 these alkaline solutions, was examined, with the result that it 

 appeared to be nil, arid, as regards the removal of moss from 

 the branches (which is one of the desirable functions of any 

 winter wash), the use of water as a solvent was preferable (VI, 73). 



The addition of larger amounts of soap to the alkaline washes 

 gave much more satisfactory results. These may be summed 

 up as follows 



