My dear Paget

I am very much obliged for your essay which has interested me greatly.¹ What indomitable activity you have! It is a surprising thought that the diseases of plants sh^d. illustrate human pathology. I have the German Encyclopædia & a few weeks ago told my son Francis that the article on the diseases of Plants would be well worth his study, but I did not know that it was written by D^r Frank, for whom I entertain a high respect, as a first-rate observer & experimentiser, though for some unknown reason he has been a good deal snubbed in Germany.²

I can give you one good case of regrowth in plants, recently often observed by me, though only externally, as I do not know enough of histology to follow out details. It is the tip of the radicle of a germinating common bean. The case is remarkable in some respects, for the tip is sensitive to various stimuli & transmits an order, causing the upper part of the radicle to bend. When the tip (for a length of about 1mm) is cut transversely off the radicle is not acted on by gravitation or other irritants, such as contact &c &c, but a new tip is regenerated in from 2 to 4 days, & then the radicle is again acted on by gravitation & will bend to centre of earth. The tip of the radicle is a kind of brain to the whole growing part of the radicle.³

My observation will be published in about a weeks time, & I w^d have sent you the book, but I do not suppose that there is anything else in the book which would interest you.—⁴

I am delighted that you have drawn attention to galls.⁵ They have always seemed to me profoundly interesting. Many years ago I began (but failed for want of time, strength & health, as on infinitely many other occasions) to experimentise on plants, by injecting into their tissues, some alkaloids. & the poison of wasps, to see if I could make anything like galls. If I remember rightly in a few cases the tissues were thickened & hardened. I began those experiments, because if by different poisons I could have affected slightly & differently the tissues of the same plant, I thought there w^d be no insuperable difficulty in the fittest poisons being developed by insects so as to produce galls adapted for them.⁶ Every character, as far as I can see, is apt to vary. Judging from one of your sentences you will smile at this.—⁷

To anyone believing in my Pangenesis (if such a man exists) there does not seem to me any extreme difficulty in understanding why plants have such little power of regeneration; for there is reason to think that my imaginary gemmules have small power of passing from cell to cell.—⁸

Forgive me for scribbling at such unreasonable length; but you are to blame from having interested me so much.—

My dear Paget | Yours very sincerely | Ch. Darwin

P.S. | Perhaps you may remember that some 2 years ago you asked me to lunch with you & proposed that I sh^d offer myself again, whenever I next come to London, I will do so, & thus have the pleasure of seeing you.—