WCP2972

[1]^1,2

Botanic Gardens

Singapore

Nov 13. 1909

Dear Mr Wallace.

Thanks for your letter of Oct 21 just received. In the matter of wind dispersal of small seeds, I have made some account of observations, & published an account of wind dispersal in the Annals of Botany of which I take pleasure to send you a copy. I have many doubts as to the dispersal of seeds not plumed or dust seeds to any distance at least in this part of the world, such seeds as Gesneraceae (excluding the plumed ones) crucifers & the like. We have many in good positions here eg Rubiac[e]ae Spermacoce etc. Now first I would [2] note the evidence in Epiphytism not only of plants of truly epiphytic character, but those which are accidentally epiphytic. On the palms in the garden one commonly finds in the trunks in the old leaf axils a number of weeds of which the seeds have got to various heights on the trunk, & grown[.] I made a study of these, listing all I found all about the gardens. With the exception of 2 plants of Phyllanthus niruri (which has explosive capsules) all were either plants where seeds were the common food of birds & bats & constantly so dispersed, or orchids & ferns or other dust seed plants, or plants with plumed seed. Spermacoce, Burmanniaceae, grasses, scrophulariaceae were all noticeably absent although the plants grew at no distance from the epiphytes trees, were [3] abundant and exceptionally thoroughly exposed to wind action. In natural epiphytes the case is the same. Gesneriads except aeschynanthus, & such like ones do never occur as epiphytes & this is not I am sure due to the habitat not being suitable[;] most will grow for a time at least anywhere. I will as an example compare Psilotum (a dust seed) with Monophyll[a]ea or Epithema. We had a plant of Psilotum compressum, in a pot in the plant house. Very soon young plants came up on trees quite a distance off. We have Epithema & Monophyll[a]ea in the same place. They have come up abundantly on the walls of that plant house where the rain runs from the plant down the walls, but have not spread 20 yards[.] Their seeds are minute[.] Again on Mt Ophir is a little Loxocarpus ⁱⁿ a very exposed spot[.] It has not reached the next mountain Gunung [Malay: Mountain] Angsi though other [4] Mount Ophir plants have!

You may perhaps remember how in our forests, be the wind ever so strong high up in the trees, there is often not a breath wher below where these small seeded Didymocarpi[,] Balsams etc grow. The air is quite still, & there is not enough to lift their seeds.

This class of plants too as I have said is absent from the oceanic islands. Christmas island is by no means over stocked with vegetation. There is room for vast additions, & that this is so is shown I trust by the rapid increase of this type of plants through the introduction of cattle of late years[.] In open steppes with the heavy northern gales I can quite understand the dispersal of seeds of this type by wind, but every thing [5] here (I have but given one or two instances) seems to show that such seeds are not as a rule borne to any distace by wind. The spreading of newly introduced arrivals & plants is sometimes very rapid, but what surprises me more is how very long it takes in very many instances for them to move any distance. Today I found two Bulimus reversus fully 300 yards from the spot this snail was first introduced to. It first appeared in the precincts of a plant house, having been I surmise introduced in plants from Manilla. This was fully 15 years ago, I think more. I have watched its progress[.] It has been plentiful for some years round the plant house & has gradually spread a few yards a year. I introduced a Gymnostachyum from Pahang in1891. It is now abundant in the garden but [6] has not got 100 yards away from the spot I first grew it in a pot! Its seeds are dispersed by a rather poor explosive arrangement.

But to wind dispersal again. It would be decidedly difficult to determine how far wind dispersed small seeds by actual observation. The best method is I think observation of the spots they appear in. The rough palm trunks are usually covered with a vegetation of all kinds of things, even seedlings of bushes & big trees, but and I think

form[?], a good test. If the wind takes the seeds of grasses, scrophulariaceae etc thereon some would certainly grow. I find such plants as Eugenia[,] Adinandra, Ficus, Melastoma[,] Clidemia, on these trees[,] all bird or bat plants, but none of the seeds you suggest & if this is so on our open grass-plots, how much less often [7] would such seeds be blown any distance in our dense forests. Most Gesneraceae are dwarf plants and ^{their seeds} would not get a rise on them, sufficient to carry them any distance I think with any wind we have here.

I when working at seed dispersal by wind was much surprised by the extremely short distance winged fruit spread than be

But you will see this in the paper I send. I think the dispersal instance of winged fruit and seed has been much overestimated. The fruits of Cumpassia [Koompassia] in as strong a wind as we have here, went actually no further than the leaves of the tree.

[8] The absence of any given plant or group of plants from an island of course may be due to the failure of the seed to grow, but it is not likely that given an island in the state of Krakatao after the eruption, waiting so to say for vegetation & otherwise as similar in soil etc to the nearest land, that some seeds at least would not germinate ie of the cruciferae, scrophulariaceae type. I know of course of the cruciferae of the Atlantic islands, but suspect these to have been taken ^there by birds[.]

However this letter is getting too long. I will try to fit up some experiments as to seed of the small type, when we next get a strong wind here, but it is naturally difficult.

& so remain | Yours sincerely | Henry N Ridley [signature]

[9] PS. In spite of the length of this I must add a post-script to say that I expect to retire in a year or two, & reluctantly return to England. I do not relish the prospects of leaving the grandeur of the tropics for dark & dirty England. The longer one lives here the more interesting the country becomes, & question after question rises up awaiting solution but life is so short that it is only when one gets near the end that one begins to see the glimmerings of the meanings of nature.

When I do come however I shall hope to see you again and be able to talk over some of the [10]³ puzzles of nature.

HNR