Aërial Roots of the Mangrove

Abstract

IN your note on a recent meeting of the Royal Botanic Society (July 30, p. 304), it is stated that the only explanation yet offered of the erect aërial roots of Avicennia nivea is that of detaining the débris and preventing the soil from being washed away. Without in any way detracting from the ingenuity and probability of Mr. Sowerby's explanation, it can hardly be admitted that this is the only explanation that has as yet been proposed. The peculiarities, both structural and physiological, of the mangrove-vegetation of the swamps of the Malayan Archipelago have been, during recent years, a special subject of investigation by botanists located at the Botanical Laboratory at Buitenzorg; the most recent and most important addition to its literature being comprised in the 22nd Heft of Luerssen and Haenlein's “Bibliotheca Botanica,” illustrated by eleven fine plates, by Herr G. Karsten. Herr Karsten points out that, in addition to the obvious mechanical function of these roots, serving as a supporting organ to attach the trees more firmly to the very loose soil in which they grow—this is especially observable in Rhizophora mangle—there is another important function performed by them, at least in a large number of the trees which make up the mangrove-vegetation, though I do not recollect that Avicennia nivea is especially mentioned. In the species examined by Karsten, these aërial roots possess very large intercellular spaces, which serve to promote the interchange of gases; and he considers it unquestionable that their chief function is to assist respiration. He therefore proposes for them the term “pneumatophores.” It would be interesting to examine the structure of the trees at the Botanic Garden in this respect. All mangrove-trees also contain large quantities of tannin, which is probably serviceable in preventing rotting. August 1.