AGKEEMENT AS TO LAKGE GENEEA 459 



think the influence of associations of this and other sorts on 

 descriptive systematists. 



On re-reading your MS., I find the same objections as 

 before, viz., that you overrate the extent of my opposition to 

 your method. My great desire was to put every possible 

 objection as strongly as I could. I did not feel myself a 

 dissenter or opponent to your views, so much as a non-con- 

 senter to them in the present state of my knowledge, nor till 

 you had weighed my objections which I thought of greater 

 weight than I do now. 



July 15 [1858]. 



The E.I.C. Examinations are cutting my time to shreds 

 which must account for some of the incoherence of the fore- 

 going. I have had more time for thinking over the subject 

 at odd half hours and have endeavoured to grapple with the 

 whole question. That point of the hypothetical behaviour 

 of large genera when on the decrease puzzles me. 



As a corollary to your law, large Natural Orders should 

 have fewer genera in proportion to species than small ; i.e. 

 fewer definable groups. Cruciferae, Compositae, Umbelli- 

 ferae and Grasses bear you out in this true no end of genera 

 are made in them, but they are bad other Natural Orders 

 are opposed. 



I think I have thought of a better reason than you give 

 for whole Nat. Ords. being worse for your purpose than local 

 Floras viz., 1. That conditions do not go on varying with the 

 area beyond a certain point ; there are limits to the combina- 

 tions of climate and soil. A genus inhabiting 1000 square 

 miles will survive such and such conditions and under their 

 influence form x species ; all these conditions may occur in 

 100 miles of the said area, and adding the other 900 miles adds 

 no more conditions. 2. Many large genera are absolutely 

 confined to the tropics or to temperate regions or to dis- 

 tricts and do not stand in the same relation to one another as 

 the mundane genera do. This I think you have expressed, 

 but not more clearly than I have. This would lead me to 

 suggest the propriety of working one or two of your Floras by 

 purging them of stragglers and such plants generally as are 

 typical of other climates and exceptional in this of stragglers 

 in short e.g. Panicum. I think this process would intensify 

 your results. 



