460 LETTEKS 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, you 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 whole. 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 smaU area, the climate and soil seem most un- 

 favourable to the germination of seeds by nature, and further 

 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 your refrigeration doctrine, to which I think I should 

 have come clumsily at last by myself as the only way of 

 accounting for the spread of European species to AustraHa. 



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 exceptioD 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 



* For Darwin's caution on this point, see his reply to this letter given 

 in M.L. i. 445. 



