My dearest F.

Your mother forgot to give me your letter of yesterday until the evening after I had written.² Remember to keep beans not above 60^o F. if possible.— Would it not be well to show Sachs effect of touching apex once lightly one side.³

If I were you I w^d not try many experiments at Wurzburg, which you could try here.

I am very glad to hear about Mustard seed; for I am very curious to learn how far apex is the governing point for movements relatively to light.— But I think you did try this here.⁴ With aerial roots it w^d be much better to cover tips (& this is easily done) with Gold-Beaters skin (I enclose some in case you like to try it) & coat some with Black paint thickly & leave others with the Gold-beaters transparent.⁵

What-ever Sachs may say, it seems to me important to prove that an aphelic organ grows quicker in dark— it is good concurrent evidence that light is only the regulator & not cause of movement.

I would use proshelic & aphelic.—if substantives can be made— Would proshelism do instead of heliotropism, & so with aphelism.— If not I think I will stick to Heliotropism & apheliotropism—to heliotropic & apheliotropic.— Ask Goebel about this—⁶

My fir-trees will on our return be ready for ligature of leading & all the lateral shoots but one.—⁷

I shall be curious hereafter to have explained your spiral theory about revolving nutation or circumnutation—⁸ It seems probable;—but remember an ellipse—often very narrow—is usual figure described.

I am getting to hate the work, & wish all radicles were deep in the earth.

Ever yours affect | C. Darwin

Do not forget Porliera⁹