507 



insect, which may clear up many hitherto-contested theories as to the 

 identity of the grape-leaf gall-louse of the United States with the true 

 root-gall lonse of France, and which is supposed to be the same insect 

 in a diftereut form, and with different habits ; the means by which they 

 can be destroyed to the best advantage, no doubt, will be of the greatest, 

 utility to the grape-growers, both of Europe and this country, especially 

 if the two are satisfactorily proved to be merely varieties of the same 

 insect. 



CHEMICAL MEMORANDA. 



By Wm. McMtRTRiE, Chemist, 



Paris aREEAT — jxs use in agriculture. — The question of the use 

 of arsenical comi^ounds in agriculture for the destruction of noxious in- 

 sects has elicited considerable discussion, and we have received from 

 our correspondents in different sections, especially those infected with 

 the Colorado })otato beetle, very many and various questions, which 

 have led us to the consideration of sevei'al points concerning it. 



Some of the farmers seem to consider that, when applied to the potato 

 crop for the destruction of the beetle, it will have an injurious and poison- 

 ous influence upon the tubers. Others fear the absorption of arsenic by 

 the tubers to a sufficient extent to be injurious to the health of the con- 

 sumer. We have also received applications for information concerning the 

 use of arsenical compounds in solution and their probable effect upon vege- 

 tation. And the question as to whether or not arsenic could be absorbed 

 and assimilated has also raised in our own minds the question whether the 

 arseniates of the alkaline earths can substitute the corresponding phos- 

 phates, all being included in the same chemical classihcatiou, in the 

 economy of plant-growth. The results of our experiments in this par- 

 ticular, though not complete, may, to a certain extent, settle the first 

 point. The full description of these experiments must be given here- 

 after, but a partial statement of the results seems pertinent here. A 

 number of boxes of soil were prepared with pure washed sand contain- 

 ing a mixture of kainit, (crude sulphate of potash,) gypsum, (sulphate 

 of lime,) and each of the boxes containing respectively the arseniates of 

 lime, baryta, strontia, and magnesia. Alongside of these boxes were 

 others prepared in a similar manner, but containing the phosphates 

 instead of the arseniates of the alkaline earths. In all of the boxes 

 pease were sown, and after ten days a large number of the seeds planted 

 in the boxes containing the arseniates had failed to germinate, and those 

 plants which had sprung up were very weak and sickly. Fresh seeds 

 were sown in those portions of the boxes in which the seeds had pre- 

 viously failed to grow, and this time a tolerably fair proportion of the 

 seeds germinated. But, as in the previous instance, they failed to 

 evince a healthy condition of growth. The seeds were sown early in 

 Augast, and on account of the frost it was found necessary to collect 

 the plants in the latter part of October, when they were just about 

 blooming. On testing specimens at different stages of growth by means 

 of ]\Iarsh's test, after having boiled the green plant with solution of 

 chlorate of potash and hydrochloric acid, not a trace of arsenic could be 

 detected. When the plants were taken up it was found that the tap- 

 root was destroyed, and that sufficient small fibrous lateral roots had 



