"I am now become mad about drops of water injuring leaves. Please ask Mr. Payne (736/3. Lord Farrer's gardener.) whether he believes, FROM HIS OWN EXPERIENCE, that drops of water injure leaves or fruit in his conservatories. It is said that the drops act as burning-glasses; if this is true, they would not be at all injurious on cloudy days. As he is so acute a man, I should very much like to hear his opinion. I remember when I grew hothouse orchids I was cautioned not to wet their leaves; but I never then thought on the subject."
The next letter, though of later date than some which follow it, is printed here because it briefly sums his results and serves as guide to the letters dealing with the subject.)
LETTER 736. TO W. THISELTON-DYER.
(736/4. Published in "Life and Letters," III., page 341.)
Down, September 5th {1877}.
One word to thank you. I declare, had it not been for your kindness, we should have broken down. As it is we have made out clearly that with some plants (chiefly succulent) the bloom checks evaporation—with some certainly prevents attacks of insects; with SOME sea-shore plants prevents injury from salt water, and, I believe, with a few prevents injury from pure water resting on the leaves. This latter is as yet the most doubtful and the most interesting point in relation to the movements of plants.
(736/5. Modern research, especially that of Stahl on transpiration ("Bot. Zeitung," 1897, page 71) has shown that the question is more complex than it appeared in 1877. Stahl's point of view is that moisture remaining on a leaf checks the transpiration-current; and by thus diminishing the flow of mineral nutriment interferes with the process of assimilation. Stahl's idea is doubtless applicable to the whole problem of bloom on leaves. For other references to bloom see letters 685, 689 and 693.)
LETTER 737. TO J.D. HOOKER. Down, August 19th, 1873.
The next time you walk round the garden ask Mr. Smith (737/1. Probably John Smith (1798-1888), for some years Curator, Royal Gardens, Kew.), or any of your best men, what they think about injury from watering during sunshine. One of your men—viz., Mr. Payne, at Abinger, who seems very acute—declares that you may water safely any plant out of doors in sunshine, and that you may do the same for plants under glass if the sashes are opened. This seems to me very odd, but he seems positive on the point, and acts on it in raising splendid grapes. Another good gardener maintains that it is only COLD water dripping often on the same point of a leaf that ever injures it. I am utterly perplexed, but interested on the point. Give me what you learn when you come to Down.
I should like to hear what plants are believed to be most injured by being watered in sunshine, so that I might get such.