460 LETTEBS TO DAKWIN, 1843-1859 
Darwin submitted a definition of the great groups into 
which flowering plants are divided. Hooker in reply defines 
these, and adds : 
If you take reproductive organs as test of highness 
or lowness, then Coniferae are top of Vegetable Kingdom; 
if you take coverings of those and neglect the organs 
themselves, 3^ou may place them below Monocots, but in 
so doing you neglect the vascular system, germinative and 
embryological characters which are all as in Dicots, not as 
in Monocots. 
P.S. — I am very busy with the Introductory Essay to 
the Tasmanian Flora, and am dealing with the Australian 
as a wdiole. The only thing that will strike you is that 
the vast majority of the trees are hermaphrodite ; this 
arises from the preponderance of arborescent hermaphro- 
dite Orders (Myrtaceae, Leguminosae) and absence of 
Amentaceous.^ 
The great preponderance of local distinct species in the 
Flora I must hook on to the destruction of seeds somehow, 
restricting the multiplication of forms. In the Swan Eiver 
Flora, where an incredible number of species are crammed 
into a very small area, the climate and soil seem most un- 
fa vom'able to the germination of seeds by nature, and fm'ther 
the most local and peculiar Order, Proteaceae, ripen very 
few seeds and are a long time about it.^ 
I however want you to print before I make up my mind 
to go into this subject. I also want you to print that I may 
take up yom' refrigeration doctrine, to which I think I should 
have coiiie clumsily at last by myself as the only w^ay of 
accounting for the spread of European species to Australia. 
It is curious that so many more European species should 
be in Australia than in Fuegia and S. Chile, especially con- 
sidering the enormous distance of Europe to Australia and 
no continuous mountains. 
^ This exception to the rule, proved in England, New Zealand, and the 
United States, that trees have their sexes separated more often than other 
plants, is noted in the first edition of the Origin, p. 100. In the sixth edition, 
the qualification is added, that ' if most of the Australian trees are dicho- 
gamous, the same result would follow as if they bore flowers with separated 
sexes.' 
* For Darwin's caution on this point, sec bis reply to this letter given 
in M.L. i. 445. 
