See "Life and Letters," II., page 89.

In the "Origin," Edition I., page 100, the author quotes Dr.Hooker to the effect that "the rule does not hold in Australia," i.e., that trees are not more generally unisexual than other plants.

In the 6th edition, page 79, Darwin adds, "but if most of the Australian trees are dichogamous, the same result would follow as if they bore flowers with separated sexes.") It is enough to knock me down, yet I can hardly think that British N.America and New Zealand should all have been theoretically right by chance.

Have you at Kew any Eucalyptus or Australian Mimosa which sets its seeds?
if so, would it be very troublesome to observe when pollen is mature, and whether pollen-tubes enter stigma readily immediately that pollen is mature or some little time afterwards?
though if pollen is not mature for some little time after flower opens, the stigma might be ready first, though according to C.C.Sprengel this is a rarer case.

I wrote to Muller for chance of his being able and willing to observe this.
Your fact of greater number of European plants (N.B .-- But do you mean greater percentage ?) in Australia than in S.America is astounding and very unpleasant to me; for from N.W.America (where nearly the same flora exists as in Canada ?) to T.del Fuego, there is far more continuous high land than from Europe to Tasmania.