Darwin-Hooker Letters : Letter from J. D. Hooker to C. R. Darwin [16? October 1864]
Hooker, Joseph Dalton
Darwin-Hooker Letters
<p style='text-align: justify;'>Morphological differences only partly define species; physiological differences, e.g., incompatibility results in <i>Primula</i>, are far more interesting.</p><p style='text-align: justify;'>T. Thomson’s review of Agardh’s muddled book ["Agardh’s classification of plants", <i>Nat. Hist. Rev.</i> (1864): 536–51].</p>