My dear Father,

Many thanks for your long letter which is very interesting & told me all I wanted.² I have been going on a twiners a bit, & I think the movement is certainly worth carefully working at. I believe you are right that nutation goes on in the free tip. I have been tracing it, like this, putting a bell glass with cylindrical sides over the shoot, & tracing the course by Pouters³ dodge of a square edge, the curve is not a simple spiral, but something like this, going on the whole spirally up but with distinct backward & downward moves, showing that all sides must be growing; I made a curve on a bell glass of a Cobaea tendril which was nutating & making one circle in an hour & it showed fine modified nutation; when it was at one end of its big circle it made 3 little clear circles each in $\frac{1}{4}$ hr & then swept across in a continuous line to make a big one again.⁴ I have read Wiesner’s thing & should not have had a glimmer of an idea of what it meant. Sachs says induction is the same as Nachwirkung or after effect.⁵ As far as I can make out he means that if a straight shoot is exposed to light on one side for a time it will bend to AC, then if the light is removed it will go on curving as AD, then if the light is brought back it will not curve more like AE but go on in the old direction— Sachs thinks very little of it he says Wiesner writes over again with much parade what is quite well known already; but Sachs is certainly severe. I must read de Vries on Epinastie & Hyponastie & I will see what Sachs says.⁶

I am afraid Gossypium does not sleep or any how very slightly.⁷ I made a mistake about Bauhinia Richardeana it has only a much divided leaf like the other species. Also I gave a name wrong it is Albizzia Zulibrissin.⁸ Here are a few more Leguminosæ

Pterolobia abyssinica shuts upwards

Cassia suffruticosa & tomentosa

Poinciana gillesia   upwards

Prosopis juliflora   upwards

Coulteria pertinata   upwards

Adenanthera pavonina— slight sideways twisting of leaves

The Adenantheras seem the only slightly new movement,

Albizzia Lebek⁹

It seems to me also that it cannot be growth or increased tension on the outer side. of a tendril, but that shortening of the inner side is the primary cause & the outer side lengthens to allow the tendril to curl up— When a tendril finds it cannot catch anything it curls up, but it would never be such an idiot as to grow violently on one side when it has no object to gain; but supposing that while it keeps itself straight it is doing work, as it were against a spring, then it would be quite natural that it should allow the spring to do what it liked when there was no object to be gained by keeping the spring stretched. I don’t see how they can distinguish between the stretching of the outer convex side & its growth. I kept Porliera in the pot for 3 or 4 days without water & the leaves were then certainly slightly shut in the morning, I then watered it & the next morning they were wide open   I will water the bed plant well.¹⁰

I will look out for some other sleepers.

Semper said he should not order the machine yet as it was a large sum for him; he showed me all over his laboratory & was very pleasant & awfully civil¹¹   He has lots of living creatures & a corresponding smell, young alligators & prairie dogs, & birds—& a fine aquarium with lots of axollotls & menobranchus & blind things from Carniola &c.¹² He doesn’t think much of Weismann’s experiments it seems to me that no German thinks much of other scientific men.¹³ Semper has a fine case of changed conditions producing an effect a Menobranchus? can be made to lay eggs just like a machine, if kept for some months in a small aquarium with few plants & then put into a large one with plenty of plants, though fed well in both cases. He has several of those great spiders (Mygales?) which seem well, he says they eat mice.¹⁴

I shall leave here about Aug 8^th I expect & I shall be awfully glad to get back

Your affec son | Frank Darwin.

Sachs has just shown me the fruit of Helvingia ruscifolia nearly related to Ivy, the petals are fleshy, purple, & full of juice like a mahonia berry, & close over the carpels so that the thing looks like a berry, it has a most beautiful bloom, it seems to me a fine case of bloom appearing on petals when they act the part of fruit. I will clean some & see if they burst in water¹⁵