=Effect of Soil, Climate and Cultivation on the Toxic Properties of Plants.= In general, wild poisonous plants are richer in either alkaloids or glucosides than the same species when cultivated, though there are exceptions. In many cases it is found that plants vary considerably in toxicity, or the percentage content of the poisonous principle, according to soil, light, moisture, etc. Solanaceous plants in particular vary in this way, and one or two instances may be given as examples. _Solanum nigrum_ varies so much that it has been regarded as harmless in one country and quite poisonous in another (p. 52).
Experiments conducted at the Arlington Experimental Farm, Virginia, showed that in 24 first-year plants of _Atropa Belladonna_ grown in 1910 the alkaloid contents of the leaves varied from 0·334 to 0·700 per cent., and averaged 0·547 per cent. In 1911 the alkaloid contents (usually the average of five pickings) of the leaves of 59 plants varied from 0·306 to 0·766 per cent., and averaged 0·532 per cent. In 1912 the alkaloid contents (commonly the average of 5 pickings) of the leaves of 57 plants varied from 0·352 to 0·768 per cent., and averaged 0·545 per cent. In individual plants at a single picking the highest alkaloid content in 1911 was 0·925 and the lowest 0·200, and in 1912 the highest was 0·882 and the lowest 0·292. (_Jour. Agric. Res._, I. 2, Nov., 1913.)
The variation in the percentage of poisonous principle was well shown in several papers read at the International Congress of Applied Chemistry held at Washington and New York in 1912 (see _Chemist and Druggist_ reports). For example, Carr stated that at the Wellcome Materia Medica Farm, Dartford, Kent, the effect of manuring on medicinal plants has been tested for some years, and the effect of the more common fertilisers on _Atropa Belladonna_ was shown by the following table:—
────────────────────────────────────┬────────────────────────────────── │Percentage of Alkaloid in Dry Stem │ and Leaf ──────────────┬───────────┬─────────┼──────┬──────┬──────┬──────┬────── │ │ │ 1906 │ 1907 │ 1910 │ 1911 │ 1912 Fertiliser │ Time of │Per acre │ 3rd │ 4th │ 1st │ 2nd │ 3rd │Application│ │year’s│year’s│year’s│year’s│year’s │ │ │plants│plants│plants│plants│plants ──────────────┼───────────┼─────────┼──────┼──────┼──────┼──────┼────── Main crop │ │ │ 0·54 │ 0·34 │ 0·61 │ 0·59 │ 0·68 Farmyard │ March │50 loads │ 0·54 │ 0·34 │ 0·61 │ 0·53 │ 0·71 manure │ │ │ │ │ │ │ Nitrate │ March & │ 2 cwt. │ 0·52 │ 0·23 │ 0·54 │ 0·46 │ 0·64 │ April │ │ │ │ │ │ Calcium │ Do. │ 1 cwt. │ │ │ 0·69 │ 0·49 │ 0·75 cyanamide │ │ │ │ │ │ │ Basic slag │ Do. │ 2 cwt. │ 0·61 │ │ 0·65 │ 0·56 │ 0·84 Superphosphate│ Do. │ 5 cwt. │ 0·46 │ │ 0·81 │ 0·49 │ 0·76 Potash │ Do. │ 5 cwt. │ 0·61 │ 0·40 │ 0·75 │ 0·53 │ 0·69 ──────────────┴───────────┴─────────┴──────┴──────┴──────┴──────┴──────