446 LETTEES TO DAKWIN, 1843-1859 



plants I should say that a high development in the scale is 

 indicated by special adaptations of organs to the discharge 

 of functions, great deviations in those organs from the type 

 upon which they are constructed. Thus Eanunculaceae 

 are low in the scale because the floral organs are apt to run 

 into one another and revert to the type (a leaf) on which 

 they are constructed because calyx and corolla are so 

 often alike stamens often reverting and the follicles present 

 little deviation from a leaf folded on itself. Hence Mono- 

 petalous flowers are higher than polypetalous, inferior 

 ovaries a higher type than superior, Dicotyledons than 

 Monocot, Exogens than Endogens, &c., &c. 



Darwin's answer is given in ' More Letters/ i. 76 : the 

 distinction he draws lies in the amount of morphological 

 differentiation and the division of physiological labour. (See 

 below, p. 463, letter of December 26, 1858.) 



Darwin had been making out various Grasses from book 

 descriptions, and sent one that baffled him for identification. 



Richmond, Sunday. 



MY DEAR DARWIN, Your grass appears to me to be 

 Festuca pratensis, and agrees as ill with the descriptions as 

 most plants appear to do. How on earth you have made 

 out 30 grasses rightly is a mystery to me. You must have 

 a marvellous tact for appreciating diagnoses. I am sure 

 that I could not have done it. I very much rejoice at your 

 feats, as it will afford us many subjects of interest in common 

 when we meet again. I think that some structural points 

 would interest you as that of the inflorescence of Grasses. 

 Amongst facts of interest which will one day be licked into 

 shape pro or con species and migration, is that of the South 

 Coast of Australia. I have just made a resume of the 

 Australian Leguminosae, about 900 species. Of these some 

 450 inhabit the South West Corner, Swan Kiver, &c., and 

 about 300 the South East (New South Wales, &c.), but there 

 are not 10 species common to both ! Now what can migra- 

 tion be about, trans-water or trans-land ? and what a 

 busy time of it Dame Nature has had in making so many 

 species, whether by creation or variation. 



I am busy at Indian Compositae. There are two very 

 common English Thistles, a small one, Carduus acanthoides, 



