430 Retrospective Criticism. 



supposed to be worth about 1000/. If sawn into veneers, it was computed 

 that the cost of labour in the process would be 750/. The weight at the 

 king's beam was 6 tons 13 cwt.] 



Art. III. Retrospective Criticism. 



On the Use of Quassia in destroying the Scale Insect. — At the time the 

 June Number of the Gardener's Magazine came to hand, I had by me a 

 paragraph, headed as above, intended for your inspection; but as your corre- 

 spondent E. O., at p. 307. of the current volume, has brought before the public 

 an easy and effectual means of destroying aphides, in the form of an application 

 of quassia chips in decoction, and also made there very similar observations to 

 my own, I will not here say more than that, in addition to his experiments 

 in this particular, I can, from my own made last autumn, assert that it is 

 effectual in destroying also another race of plant pests, viz. the scale insect 

 (Aspidiotus sp.), probably the whole of the genus ; but my experiments have 

 been directed more particularly against that species which infests succulents, 

 especially the genera Mesembryanthemum, A'picra, Haworthza, &c. 



My mode of application differs from that of your correspondent, the 

 decoction being brushed carefully and entirely over the plants infected, 

 instead of being applied with a syringe. Many of the scale insects will, at 

 the time it is applied, fall from the plant, simply from being dislodged by the 

 brush (which should be soft rather than otherwise, to avoid, as far as possible, 

 bruising the plant), but the greater portion of them will remain on the plant 

 for some time ; they will, however, on examination a few days after the appli- 

 cation, be found to be lifeless ; these will, in the end, dry up, and scale off. 



With your correspondent I believe also that quassia renders the plant, at 

 least for a time, obnoxious rather than agreeable to these invaders. 



I had, until the middle of May last, thought that my first washing, which 

 was given last autumn had entirely eradicated the scale, and so, I believe, it 

 did effectually destroy the then existing generation : but I find now that a 

 new race, all of about equal size, and in all probability of equal age, appear 

 upon my plants thus previously cleansed, which shows that a single washing 

 is not sufficient tc entirely subdue the scale for a year, unless applied in June 

 or July instead of the autumn ; in which case, I should say, one washing yearly 

 would be sufficient, and in all probability would, in a few years, entirely 

 extirpate them. 



However anxious we may feel to impart any knowledge we may gain from 

 practice, or from intimacy with the effects of certain articles in destroying or 

 even retarding the increase of any enemies to plants, still I think it but our 

 duty to caution the young gardener against trusting too much to prescribed 

 remedies, and recommend him to practise diligently the old cure of picking off 

 vermin (some kinds of which, I cannot but say, are better formed for the 

 practice than others, as the mealy bug (Coccus Adonidum Linn.), and some 

 of the larger species of scale insect) from the plants with his fingers, or any 

 other means that his ingenuity may suggest, as being better suited for the 

 purpose ; taking care, at the same time, not to crush the insects on the leaves, 

 &c, of the plants, as they almost without exception, injure and disfigure 

 the plant ; and he may rest assured that he will keep them in subjection. I 

 would nevertheless wish him, should his mind be so disposed, to enjoy the 

 assistance of any such remedies as he may think fit ; and also let him proceed, 

 without restriction, with enquiries and experiments that he may consider 

 likely to turn out in any way beneficial to his profession, and doubtless, in 

 many instances, good will come from it. — W. H.B. -Oxford, June 3. 1842. 



On Worming in Com. — In the February Number of the Magazine, you have 

 copied from the Cambridge Chronicle an account of a field of corn which was 



