The first claim to the discovery of boron in plants was put forward in 1857 by [Wittstein and Apoiger], who carried out investigations on the Abyssinian Saoria (seeds of Maasa or Maessa picta, N.O. Primulaceae[12]). In the course of analyses a crystalline mass was obtained which was found to contain chlorine, phosphoric acid, lime, and boric acid. The discovery apparently attracted little attention and for about another thirty years the matter was again allowed to sink into oblivion. Then it came to the front again, and from 1888 onwards one investigator after another demonstrated the presence of boron in various plants.
In 1888 [Baumert] detected boron in French, German, and Spanish wines without exception, while [E. O. von Lippman (1888)] demonstrated it in sugar must and also in the leaves and root of the sugar beet. In the latter case the reactions were so definite that the presence of more than a minimal amount of boric acid was conjectured.
[Crampton (1889)] tested various fruits, but while he found boron in every part of the watermelon, he could get no reaction with apples or with certain samples of sugar cane. He predicted, however, that the occurrence of boron would prove to be more general in the plant kingdom than had previously been supposed. The next year (1890) [Hotter] extended the work on fruits, testing for boron in the fruits, leaves, and twigs of certain plants, and finding it in the apple, pear, cherry, raspberry, fig, and others. His results indicated that fruits are relatively rich in boron. Later on (1895) [Hotter] carried his experiments further, and he stated that stone fruits are richer in boric acid than are berries and pomes. The accumulation of boron is in the fruit itself, the other parts of the plant containing little. The quantities of boric acid found in the ash of the various fruits ranged from ·58% in the “Autumn Reinette” apple to ·06% in figs. [Bechi] had previously (1891) detected boron in the ash of figs, love-apple, and rubus fruits from Pitecio, but he attributed this to the presence of boric acid or borates in the soil at the place.
[Passerini (1891)] found traces of boron in the stems of chickpea plants, while in 1892 [Brand] determined boric acid in the ash of beer. In consequence of this various samples of hops were ashed without the addition of any alkali, and then the ash was distilled with sulphuric acid and methyl alcohol. When tested all the hops showed relatively large quantities of boric acid in comparison with beer, hence he argued that the boric acid in beer is derived from the hops. Boron was discovered in various parts of the hop plant—in the clusters, leaves, pedicels, and stems.
[Jay (1895)] analysed many plants and plant products grown in various soils and waters, and arrived at the conclusion that boron is of practically universal occurrence in the plant world. Of all vegetable liquids wines are the richest in this constituent, the amount varying from ·009 gram to ·33 gram per litre. He confirmed Hotter’s statement as to the richness of fruits in this substance, finding from 1·50–6·40 grams in 1 kgm. of ash. Chrysanthemums and onions, amongst other plants, are well off in this respect, containing 2·10–4·60 grams per kgm. of ash. Jay also found that the plants vary in their capacity for absorbing boric acid, those which do so the least easily being Gramineae (as wheat, barley, rice), mushrooms and watercress, the quantity in these plants never exceeding ·500 grams per kgm. of ash.
Of all the workers upon boron, Agulhon has done the most to extend and concentrate our knowledge of the subject. He used the most refined, up-to-date methods for the detection and estimation of boric acid, and so determined its presence in many plants, including angiosperms, gymnosperms, ferns, algae, and fungi. Tobacco is so rich in boron that it can be detected in the ash of one cigarette. Among the plants tested, the highest percentages of boric acid were found in Betula alba (1·175% of ash) and Laminaria saccharina (·682% of ash), the lowest in Cannabis sativa (·123% of ash). Generally speaking annual plants and parts of plants seem to have the least boron in the composition of their ashes. In one and the same plant the durable parts like bark and wood are richer than the leaves, even in evergreen trees. He indicated that plants seem to have a great affinity for boron, as even when plants are grown on soils in which the boron is practically indetectable they always seem to extract an appreciable quantity of the element.
From the foregoing results it is evident that boron is very widespread in the vegetable kingdom, entering into the composition of many plants in all the great classes. A general impression obtains that its distribution is universal, and that it will ultimately prove to enter into the composition of practically every plant, as the scope of the analyses is widened and as methods of detection are improved. On the other hand, Agulhon is inclined to think that boron may be a “particular element,” characteristic of certain groups of individuals or of life under certain conditions. The series of individuals differ among themselves as to their particular needs of nutriment (in the widest sense) and doubtless each group has special need of particular elements, a need that is possibly correlated with morphological and chemical differences. It may well be that boron is one of these elements, associated with certain vital functions in a way as yet unexplained, though it may possibly be found to play some part in the formation of vascular tissues, since it is most abundant in bark and lignified parts.