My dear Father,

I have been horribly idle about sleeping plants for you but I will really have a good look   it is quite easy; I have seen a Zygophyllum fabago which sleeps pretty well 2 leaflets moving vertically upwards.² Porliera seems to be a different species; the twig you sent has very much the look of mine but has only 8 or 9 prs of leaflets & that gives it a dumpy look compared with yrs.³ I havn’t made it out properly— It certainly sleeps— twigs in water in the diffused light of this room are open all morning & shut early about 3   They were open in a dark cupboard after about 24 hrs. A twig kept quite under water in blazing sun out of doors is open when the plant in bed has shut leaves. Under a bell glass in a glass of water & standing in a plate of water it remained open in full sunlight   It seems to me it must depend on dampness but I half think it depends on being richly supplied with water, as a twig is in a a glass of water; as mine does not seem the same species I will try some more things.

The oats have only just begun to germinate I shall do some to day—⁴ Sachs⁵ made a calculation & said that at the most the little tip that appears at first could only manufacture make $\frac{6}{1000}$ of a milligramm dry weight in a day by assimilating; (a milligramm = ^1/70th grain). Germinating seeds do not gain in weight he says.

PM   I have cut sections of a young oat $\frac{1}{5}$^th inch above the ground—& it has chlorophyll in it, Sachs looked & said it was chlorophyll but rather yellow, & therefore not fully developed: Only 4 or 5 oats have come up as yet & this was the smallest—I can get younger ones tomorrow morning I hope—sections is much better than alcohol which I always thought bosh.

Since writing about Porliera this morning I found another Porliera same species but in a pot & not in open ground & its leaves were wide open while the one in ground were shut. Sachs on theoretical grounds says the one in the bed gets more water, but I asked the gardener privately & he on practical grounds says he waters the pot-plant every day & never the bedded out one.

Yr affec son | F Darwin

Many thanks about my proofs

I will write to printers about 50 copies at once⁶