The specimens of oats on which these analyses were made were from different districts of country, grown on soils of different quality, and were, further, of different varieties; and yet they show, on the whole, a remarkable similarity in the proportion of ash in each part, and indicate that there is a normal quantity belonging to it. Such a series of analyses also affords the most convincing proof that the inorganic matters cannot be fortuitous, and merely absorbed from the soil along with their organic food, as the old chemists supposed, because, in that case, they ought to be uniformly distributed throughout the entire plant, and not accumulated in particular proportions in each individual organ.
Not only does the proportion of ash vary in the different parts of a plant, but even in the same part it is greatly influenced by its period of growth. The laws which regulate these variations are very imperfectly known, but in general it is observed that during the period of active growth the quantity of ash is largest. Thus, it has been found that in early spring the wood of the young shoots of the horse-chesnut contains 9·9 per cent of ash. In autumn this has diminished to 3·4, and the last year's twigs contain only 1·1 per cent, while in the old wood the quantity does not exceed 0·5. Saussure has also observed that the quantity of ash diminishes in certain plants when the seed has ripened. Thus, he found that the percentages of ash, before flowering, and after seeding, were as follows:—
| Before flowering. | With ripe seed. | |
| Sunflower | 14·7 | 9·3 |
| Wheat | 7·9 | 3·3 |
| Maize | 12·2 | 4·6 |
On the other hand, the quantity of ash in the leaves of trees increases considerably in autumn, as shown by this table:—
| Per-centage of ash in | ||
| May. | September. | |
| Oak leaves | 5·3 | 5·5 |
| Poplar | 6·6 | 9·3 |
| Hazel | 6·1 | 7·0 |
| Horse-chesnut | 7·2 | 8·6 |
In general, the proportion of ash appears to increase as the plant reaches maturity, and this is particularly seen in the oat, of which very complete analyses have been made at different periods of its growth:—
Proportion of Ash in different parts of the Oat at different periods of its growth.
| Date. | Stalks. | Leaves. | Chaff. | Grain with husk. |
| 2d July | 7·83 | 11·35 | ... | 4·91 |
| 9th July | 7·80 | 12·20 | ... | 4·36 |
| 16th July | 7·94 | 12·61 | 6·00 | 3·38 |
| 23d July | 7·99 | 16·45 | 9·11 | 3·62 |
| 30th July | 7·45 | 16·44 | 12·28 | 4·22 |
| 5th August | 7·63 | 16·05 | 13·75 | 4·31 |
| 13th August | 6·62 | 20·47 | 18·68 | 4·07 |
| 20th August | 6·66 | 21·14 | 21·07 | 3·64 |
| 27th August | 7·71 | 22·13 | 22·46 | 3·51 |
| 3d September | 8·35 | 20·90 | 27·47 | 3·65 |
The increase is here principally confined to the leaves and chaff, while the stalks, which owe their strength to a considerable extent to the inorganic matters they contain, are equally supplied at all periods of their growth. In the grain only is there a diminution, but this is apparent and not real, and is due to the fact that the determination of the quantity of ash, as made on the grain with its husk, and the former, which contains only a small quantity of mineral matters, increases much more rapidly in weight than the latter, when it approaches the period of ripening, and it is accordingly during the last three weeks of its growth that this diminution becomes apparent.
The nature of the soil has also a very important influence on the proportion of mineral matters, and of this an interesting illustration is given in the following table, which shows the quantities found in the grain and straw of the same variety of the pea grown on fourteen different soils:—