My dear Father

Here are some more sleepers²

Oxalis latifolia like Acetisella

O. variabilis— ditto but has 4 leaflets

Lotus Gebelia sleeps like a Lotus

Erythrina spathacea— an end leaflet & 2 lateral ones which all drop vertically

E. princeps— ditto

Albizzia Zulu brizzia, like A lopantha

Bauhinia discolor; the leaf is not quite divided into two leaflets but is so but shuts upwards lik B. Richardiana. This plant looks very sick & shuts up very badly, but B. forficata has similar leaves & shuts up well.

Cassia glauca— {like a Cassia outside in

Uraria lagopus (Leguminosæ) end & 2 lateral leaflets drop down vertically not outside-in, but simply   Leaflets grow so close together & are so thick that they looked asleep but are not altered by day

Coesalpina echinata shuts upwards ³

Sachs idea about climbing plants is something like this. He thinks one ought to distinguish clearly between the revolving nutation (which is only in order to find a support as you say) & the growth which goes on when the shoot has once caught a support.⁴ With a tendril the difference is quite clear, the tendril swings round till it finds a support & then all the growth (or alteration in length from altered tension) is concentrated on one side & the tendril curls up. When a twining shoot has wound round a support as far as it can, it would be much more economical of it to confine the most rapid growth to the outside only. Both cases seem to me capable of fitting in with your theory of circumnutation ceasing when the plant wants to bend in a special direction   I can’t find in your book an experiment in which the nutation ceased when a plant was turned up side down, I thought that nutation ceased in order to let all the growth to turn into geotropism.⁵ Your theory ought to be called the conservation of energy—I believe it will be splendid. I should like to know if you made many observations as to whether tendrils are geotropic or not, most seem not to be much so. Perhaps I havn’t read your book carefully enough, you often say that the circumnutation is in order to find a support, but you dont distinguish the growth afterwards I think. There is one machine we must have. A strong horizontal axis about 2 feet long which goes round by clock work slowly so that geotropism is quite excluded. We will get Jemmy to design one, the one here is far from well made.⁶

I am rather surprised at the results of my experiments on bendibility of grass stalks. If you take the cylindrical flowering stalk of grass while still green & keep it 2 or 3 days till the protoplasm in it is certainly dead, then if you test its bending strength as it is & then when it is saturated with water, it is always stronger in the wet state   But ripe white stalks which have been in the laboratory for years are always stronger dry   The same thing seems to hold with wood freshly cut sticks are stronger wet, old dry sticks are stronger dry.⁷

There have been several days heavy rain & now the Porliera in the flower bed is as open as the one in the pot. I will get the pot one in & keep it dry & see. I will have a look at the stomata, only I don’t know quite whether you mean the number of them or what. I cut some sections & the cuticle is decidely thick I should say—⁸

I find that if an already twined plant is turned upside down the last turn unwinds itself—did you ever see this. I forgot to say how glad I am the maize act so well— I like hearing about yr work v much—⁹

Yr affec son | Francis Darwin

Please remember the printing machine— Tho’ I have no doubt that you have an enormous pincers with a small bit of paper & ‘printing machine’ written in red pencil¹⁰