My dear Sir

I thank you for your letter which has interested me much; though alas! it does not aid me about roots growing in an abnormal direction when growing from a part abnormally developed.¹ Your investigation seems to have been made with great care

I can throw no light on your problem.² In such cases I have imagined some such steps as the following. That the parent species laid its eggs in plants belonging to various families, perhaps allied ones, at least with tissues of the proper texture, not poisonous &c,— that a fluid accompanied the deposition of the eggs and that this caused a slight abnormal growth of the tissues in certain families alone, and that such growth was advantageous to the larvæ,— that these larvæ inherited the taste of their parents which led the latter to select the particular plant in question,— and lastly that the fluid accompanying the eggs was increased in quantity or in intensity from being beneficial to the insect, until regular galls were formed. But all this is mere idle speculation.

I remain, with many thanks | Yours faithfully | Ch. Darwin