JvH will help with expression queries. Considers CD’s investigation highly important and original. Sends list of men to whom he is sending copies of the questions.

The theorem is one of the consequences of the Julius Plücker system. Comments on JH's proposed method.

Thanks CD for new edition of Origin [4th ed. (1866)].

Comments on CD’s criticism of the harsh tone of Generelle Morphologie. Thinks he may have harmed himself but not the cause. Believes a radical reform of the science necessary, and since most scientists take a prejudiced view of the matter, a vigorous attack is essential.

Describes his travels in Canaries, Spain, and France.

Sends Fritz Müller’s address; has sent him Insular floras [pamphlet].

Agrees reluctantly to write obituary notice of William Whewell; wishes he had been asked earlier.