353 
Ridley . — On the Dispersal of Seeds by Wind, 
verandah, 17 feet high, where there was no wind, fell vertically for 5 or 6 
feet before beginning to rotate, and lit within 6 feet of the place where they 
would have fallen had they had no wings. 
If we assume that a tree flowers and fruits at 30 years of age and the 
fruits are disseminated to a distance of 100 yards, that the furthest fruits 
always germinate and so continue in one direction, it will be seen that 
under such most favourable circumstances the species can only spread 
300 yards in 100 years, and would take 58,666 years to migrate 100 miles. 
This seems an extraordinarily slow rate of migration, but I believe I have 
much overrated the rapidity. Occasional increases might occur, such as 
the falling of a seed on a log drifting down a stream, or into the stream 
itself ; but there are very few or no streams in the hilly slopes of the 
peninsula which are strong enough to carry the seed. Again, excessively 
violent storms of wind might carry them further than usual, but such 
storms are nowadays at least very rare. I have seen these Dipterocarpeae 
in fruit during as violent wind storms as we ever have, and even then the 
fruits did not fly 100 yards. Allowing for all these possibilities, it will 
be seen that in these calculations I have estimated the flight at 100 yards, 
whereas few fruit have been found more than 40 yards from the tree, 
nor have young trees of any age been found at a much greater distance. 
Further, in the progress of the species it has been assumed that the very 
furthest fruit in one direction have developed into trees, whereas it usually 
happens that bad seed drifts further than the heavier fertile seed, and 
it is also assumed that the wind always blows violently in the same 
direction when the tree is in fruit, which is not always the case ; again, 
in the exceptional cases in which these fruits were found at upwards of 
too yards from the tree, the tree was very much taller than the surrounding 
vegetation, and had a clearer line of flight than it would have had in the 
primaeval forest, where many trees would be on the same level, and their 
foliage would check the flight from the adjacent trees ; and again, trees 
of thirty years of age being comparatively short would get much less of the 
wind than the taller century-old trees, and their fruit would certainly take 
a shorter flight. 
The Malay Peninsula consists to a large extent of hilly country, the 
hills rising to a height of 7,000 feet, but Dipterocarpeae are not met with 
much above 2.500 feet altitude. The hills, and indeed the whole country 
where these plants occur, are densely wooded, and it might be suggested that 
the fruits would fly to greater distances down the hill slopes in heavy 
gales. This might be so ; but it must be remembered that in its migrations 
a species would have to fly uphill quite as often as it flew down, and its 
progress uphill would be proportionately slower. Taking all these facts 
into consideration, it would not seem that I have under-estimated the time 
taken by a Dipterocarpous tree to migrate a hundred miles, but that on 
