To W. T. Thiselton-Dyer   4 December 1873

My dear Mr Dyer

As Hooker is so busy I sh^d be very much obliged if you could give me the name of the enclosed poor specⁿ. of Cassia. I want much to know its name, as its power of movement, when it goes to sleep, is very remarkable. Linneus I find, was aware of this.¹

It twists each separate leaflet almost completely round, so that the lower surface faces the sky, at the same time depressing them all. The termals² leaflets are pointed towards the base of the leaf. The whole leaf is also raised up about 12^o.

When I saw that it possessed such complex powers of movement, I thought it w^d utilize its power to protect the leaflets from rain. Accordingly I syringed the plant for 2 minutes, & it was really beautiful to see how each leaflet on the younger leaves twisted its short sub-petiole, so that the blade was immediately directed at an angle between 45^o & 90^o to the horizon.³ I c^d not resist the pleasure of just telling you why I want to know the name of the Cassia. I sh^d add that it is a greenhouse plant— I suppose that there will not be any better flowers till next summer or autumn.

Forgive this trouble, & believe | me Yours very sincerely | Ch. Darwin