1866.] NAGELI ON SPECIES. 235 



clear to me that a plant, with its leaves placed at some par- 

 ticular angle, or with its ovules in some particular position, 

 thus stands higher than another plant. But I must apologise 

 for troubling you with these remarks. 



As I much wish to possess your photograph, I take the 

 liberty of enclosing my own, and with sincere respect I re- 

 main, dear Sir, Yours faithfully, 



Ch. Darv/in. 



[I give a few extracts from letters of various dates show- 

 ing my father's interest, alluded to in the last letter, in the 

 problem of the arrangement of the leaves on the stems of 

 plants. It may be added that Professor Schwendener of 

 Berlin has successfully attacked the question in his'Mechan- 

 ische Theorie der Blattstellungen,' 1878. 



To Dr. Falconer. 



August 26 [1863]. 



" Do you remember telling me that I ought to study Phyllo- 

 tAxy ? well I have often wished you at the bottom of the sea ; 

 for I could not resist, and I muddled my brains with dia- 

 grams, &c., and specimens, and made out, as might have 

 been expected, nothing. Those angles are a most wonderful 

 problem and I wish I could see some one give a rational ex- 

 planation of them." 



To Dr. Asa Gray. 



May II [1861]. 



*' If you wish to save me from a miserable death, do tell 

 me why the angles \, \, f, f, &c , series occur, and no other 

 angles. It is enough to drive the quietest man mad. Did 

 you and some mathematician * publish some paper on, the 

 subject } Hooker says you did ; where is it .^ 



* Probably my father was thinking of Chauncey Wright's work on 

 Phyllotaxy, in Gould's 'Astronomical Journal,' No. gg, 1856, and in the 

 ' Mathematical Monthly,' i85g. These papers are mentioned in the ' Let- 

 ters of Chauncey Wright.' Mr. Wright corresponded with my father on 

 the subject. 



