i868 i88i] MOVEMENTS OF PLANTS 415 



uniformly cloudy. A bristle was gummed to one cotyledon, Letter 743 

 and beyond it a triangular bit of card was fixed, and in 

 front a vertical glass. A dot was made in the glass every 

 quarter or half hour at the point where the end of the bristle 

 and the apex of card coincided, and the dots were joined 

 by straight lines; The observations were from 10 a.m. to 

 8.45 p.m. During this time the enclosed figure was de- 

 scribed ; but between 4 p.m. and 5.38 p.m. the coty- 

 ledon moved so that the prolonged line was beyond the 

 limits of the glass, and the course is here shown by an 

 imaginary dotted line. The cotyledon of Priimila sinensis 

 moved in closely analogous manner, as do those of a Cassia. 

 Hence I expect to find such movements very general with 

 cotyledons, and I am inclined to look at them as the founda- 

 tion for all the other adaptive movements of leaves. They 

 certainly are of the so-called sleep of plants. 



I hope I have not bothered you. Do not answer. I am 

 all on fire at the work. 



I have had a short and very prosperous note from Asa 

 Gray, 1 who says Hooker is very prosperous, and both are 

 tremendously hard at work. 



To H. Muller. Letter 744 



Down, Jan. ist [1878?]. 



I must write two or three lines to thank you cordially for 

 your very handsome and very interesting review of my last 

 book 2 in Kosmos, which I have this minute finished. It is 

 wonderful how you have picked out everything important in 

 it. I am especially glad that you have called attention to the 

 parallelism betwen illegitimate offspring of heterostyled plants 

 and hybrids. Your previous article in Kosmos* seemed to 

 me very important, but for some unknown reason the german 

 was very difficult, and I was sadly overworked at the time, so 

 that I could not understand a good deal of it. But I have 

 put it on one side, and when I have to prepare a new edition 

 of my book I must make it out. It seems that you attribute 



1 " Hooker is coming over, and we are going in summer to the Rocky 

 Mountains together, according to an old promise of mine." Asa Gray to 

 G. F. Wright, May 24th, 1877 (Letters of Asa Gray, II., p. 666). 



2 Forms of Flowers, 1877. H. Miiller's article is in Kosmos, II., p. 286. 



3 Kosmos, II., pp. u, 128. See Forms of Flowers, Ed. II., p. 308. 



