This mountain species of Fiji, which I may name Barringtonia seaturæ, has the general habit of B. racemosa, with which the natives persisted in linking it; whilst the fruit and foliage come nearer to those of B. edulis. The leaves are entire, taper at the base, and have a petiole 1 inch long. The fruits are oblong, at least 3 inches in length, and are obscurely angled.
It would appear from Schimper’s description (p. 173) that the fruits of the Malayan Barringtonia excelsa possess both the hard stone-shell of the inland Fijian species and the dry air-bearing fibrous husk of the littoral species. This is of special interest, since the tree is both a coast and an inland species.
The following notes on the structure of the seeds of Barringtonia were made whilst I was drifting about in my canoe in the creeks of the Rewa delta in Fiji; and whatever may be their deficiencies they have the merit of having been written in the home of the plants.... When we cut across a seed like that of B. racemosa or B. speciosa, we observe that the different parts of the embryo are indistinguishable, being united into a homogeneous, firm, fleshy mass. But if we look closely we notice a central fusiform portion marked out from the surrounding parts by a faint line, along which a delicate membrane of vascular tissue has been developed. When “germination” begins, though, as the reader will subsequently perceive, this term is here hardly appropriate, the real nature of this singular structure becomes more apparent, as is indicated in the accompanying figure. The central fusiform portion proves to be the young plant without cotyledons and growing at either end to form the root and the stem. The delicate investing membrane becomes thicker and more apparent as germination proceeds, extending upwards and downwards with the growth of the stem and root and forming a cortical covering in either case. The investing fleshy portion of the seed, which is now separable with the fingers, remains attached to the lower part of the seedling for some time, being evidently a source of nutriment, and gives a bulbous appearance to the young plant. Young bulbous plants of B. racemosa, 1 to 2 feet high, are very common on the edge of Fijian mangrove swamps where the parent tree thrives. The seedlings of B. speciosa have the same appearance, but the outer fleshy part of the bulb is not so thick.
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B. racemosa., B. speciosa.
Diagrams illustrating the structure of the growing seeds of Barringtonia (two-thirds the natural size). That of B. speciosa represents a seed removed from a fruit displaying the young plant protruding two or three inches. That of B. racemosa represents the lower end of the seedling when the plant is eighteen inches high.
- a = the exorhiza.
- b = the neorhiza invested by the medullary sheath.
This structure of the seeds of Barringtonia speciosa and of B. racemosa was for a long time meaningless to me, until one day, whilst seated on the banks of the Lower Rewa, with a number of the sected seeds and bulbous seedlings gathered around, I reflected that the fruits of the latter species that floated past me in the river-drift were nearly always germinating. This called up “vivipary” to my mind; and as I looked at the Rhizophora seedlings dangling from the branches of the mangrove-trees close by, it occurred to me that this seed-structure might be the result of a lost viviparous habit. One apparently had to deal here not with an ordinary seed containing an embryo in the midst of albumen, but with a seed in an arrested stage of germination surrounded by a body that might perhaps prove homologous with the “cotyledonary body” of Rhizophora. The process of development that goes on without a break in Rhizophora, from the fertilisation of the ovule to the detachment of the seedling from the branch, was here, as I considered, arrested after germination had begun, but before the protrusion of the seedling from the fruit. With nearly all plants, as I reflected, there is a rest-stage of varying length, which might be called the seed-stage. With the mangrove-genera, Rhizophora and Bruguiera, I had convinced myself by a long series of observations, the results of which are given in [Chapter XXX.], that this rest-stage does not exist. It occurs, I argued, in Barringtonia, but only after germination has begun, and, therefore, displaced when compared with the typical seed-stage of most plants.
In this connection it may be noted that a difference in germinating behaviour might be expected between the two shore species on account of their difference in stations, Barringtonia speciosa growing on the sandy beach, and B. racemosa in the wet ground around a mangrove-swamp. There is a strong suspicion that the rest-stage in B. racemosa is very short, though I never found germination in progress on a tree (see [Note 37]). There is no doubt, on the other hand, that the rest-stage of B. speciosa is often, as with most other plants, very long. This, then, was my lesson from the Barringtonia fruits on the banks of the Rewa, and the question arose whether this interpretation of these curious seed-structures accorded with the opinion formed of their nature by botanists.