To Ernst Haeckel   12 February [1878]¹

My dear Friend

I thank you sincerely for all your most kind words & good wishes on my birth-day.² My health has been better of late, & I am able to do every day what I consider a fair amount of work, but what you would consider a mere trifle. Considering my age it will be the more prudent course for me not to attempt to write on large & difficult subjects of a general nature, but to use my remaining strength in studying small special points, & thus to aid, as far as I can, the noble cause of science. To you & others must be left the extending & fortifying the principles of Evolution.— I am now working with the aid of my son Francis, chiefly on the growth, movements & development of seedling plants; & we have observed some new & curious facts.—³

I rejoice to hear that you are well, & that you are hard at work, about which I did not in the least doubt. As you say time time is what is wanted most.—

With all good wishes to you & yours & with many thanks | Yours very sincerely | Charles Darwin