To Edward Frankland   8 February 1879

My dear D^r. Frankland

The case stands thus: we find that drops of water left standing for some days on certain leaves injured them, & afterwards my son Francis found that water left on leaves, or leaves immersed in water (with their stalks outside) in most cases made the water alkaline.¹ When such was boiled down, the residue heated to redness & then redissolved, the solution was still alkaline. This shows that it cannot be Ammonia. There is a wide difference in the degree of alkalinity when different species of plants are tried; & if I remember rightly none in a few cases; but my son is away from home at present.—² What we are very anxious to learn is what is the alkali in the water; & it is exceedingly kind of you to have it analysed.— I presume that it will be impossible to give the quantity of alkali.— As yet we have found no notice of any such phenomenon having been observed, excepting that Sachs says that dew on grass is alkaline, but he did not ascertain whether this was due to ammonia.—³ We suspect, naturally, potash, & it seems to us a strange thing if a substance which is considered so valuable a manure is secreted by the leaves.— I sh^d. have said that the water becomes alkaline when the plants are kept in the dark.—

With very true thanks | Yours sincerely | Ch. Darwin