My dear Hooker

I am extremely obliged for the plants, & I do hope not to give any more trouble to Kew for a long time.— Pray thank Dyer cordially about the geotropic plants: we have now excellent materials if we can make out anything about geotropism.² Most, indeed nearly all, of the plants shall be returned in due time. But the geotropic ones must be kept until they make fresh growths.

It is very curious how differently plants withstand frost. Most of the Cassias are extraordinarily sensitive, whereas a seedling of C. pubescens will withstand quite a sharp frost; & so in many other cases.³ This gives us infinite trouble for we cannot judge except by graduated trials, how long to expose any plant so as to injure without killing it

Ever yours | Ch. Darwin