362 BOTANY [CHAP. XI 



Letter 685 leaflets soon open. How is this with the native plants during 

 a windy day ? I find that some other plants for instance, 

 Desmodium and Cassia when syringed with water, place their 

 leaves so that the drops fall quickly off ; the position assumed 

 differing somewhat from that in the so-called sleep. Would 

 you be so kind as to observe whether any [other] plants place 

 their leaves during rain so as to shoot off the water ; and if 

 there are any such I should be very glad of a leaf or two to 

 ascertain whether they are coated with a waxy secretion. 1 



There is another and very different subject, about which I 

 intend to write, and should be very glad of a little information. 

 Are earthworms (Lumbricus) common in S. Brazil, 2 and do 

 they throw up on the surface of the ground numerous castings 

 or vermicular masses such as we so commonly see in Europe? 

 Are such castings found in the forests beneath the dead 

 withered leaves? I am sure I can trust to your kindness to 

 forgive me for asking you so many questions. 



To F. Mullen 



Letter 686 Down, July 24th, 1878. 



Many thanks for the five kinds of seeds ; all have germi- 

 nated, and the Cassia seedlings have interested me much, and I 

 daresay that I shall find something curious in the other plants. 

 Nor have I alone profited, for Sir J. Hooker, who was here on 

 Sunday, was very glad of some of the seeds for Kew. I am 

 particularly obliged for the information about the earthworms. 

 I suppose the soil in your forests is very loose, for in ground 

 which has lately been dug in England the worms do not come 

 to the surface, but deposit their castings in the midst of the 

 loose soil. 



I have some grand plants (and I formerly sent seeds to 

 Kew) of the cleistogamic grass, but they show no signs of 

 producing flowers of any kind as yet. Your case of the 

 panicle with open flowers being sterile is parallel to that of 

 Leersia otyzoides. I have always fancied that cross-fertilisation 

 would perhaps make such panicles fertile. 3 



1 See Letters 737-41. 



2 F. Miiller's reply is given in Vegetable Mould, p. 122. 



3 The meaning of this sentence is somewhat obscure. Darwin 

 apparently implies that the perfect flowers, borne on the panicles which 

 occasionally emerge from the sheath, might be fertile if pollinated from 

 another individual. See Forms of Flowers, p. 334, 



