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Darwin Correspondence Project

From F. J. Cohn   26 December 1880

Breslau

26 Dec. 1880

My dearest Sir

I can not let finish the year before I did send you my kindest thanks for the admirable present you forwarded to the whole scientific world as well as to myself.1 It is a fresh leaf to the wreath you have gained in the battle of science, evergreen as all the other’s which adorn your brow. Immediately after having received your book, I went about studying and repeating the principal experiments upon which you have founded your theory of circumnutation; of course I succeeded in ascertaining the curious curves the apex of a growing plant describes; as for your experiments about the sensitive qualities of the top of the radicle, most of your results were not foreign to me as I was engaged many years ago with studying the germination of seeds (my inaugural dissertation treats a “symbola ad seminis physiologiam, and the researches of Ciesielksy were made in my laboratory,);2 several important facts you did discover, I am about of ascertaining by repetition of your experiments. I wish, I could personaly discuss with you the many questions your book arouses, for to write about requires rather a book than a letter. In the whole I agree totally with you; I am quite sure that in plants exist tissues—which are only sensitive and transmit a stimulus to other tissues which are not sensitive but contract or swell by irritation. But I am not convinced that the theory of alternative turgenscence which you adopt for the circumnutation and other movements, does touch the truth, as you and most German physiologists accept.3 If I am not mistaken the force of movements does not dwell upon the quantity of water but upon the quality of protoplasm; the latter, in plants not less than in animals, is the truly contractile substance; and all theories which propose an essential difference between the movements of plants and animal’s cells, walk out of the right way.4 As far as my own observations go, which however, I confess, are not yet concluding, the movements of vegetable tissues (circumnutation, heliotropism etc) depend upon changes in the shape of the protoplasmic bodies of the cells (they become longer but thinner etc.) without change of volume (conservative of turgescence) or the changes of turgensie are only secondary ones. The changes of shape are conformable to some purpose or useful to the plant and therefore acquired by heredity:— But this is a theme for a long dissertation and so I refrain from; I may only add that my views repose mostly upon the study of unicellular plants where the biological facts are more palpable than in the higher and more complicated classes (cf. Oscillaria, a very fine speciman of circumnutation).5

I don’t know if I should dare to express how much I admire in your last book as much as in your former, all the qualities of a great biologist and philosopher

May to you be reserved a long series of happy years for the benefit of human knowledge. So I send you my kindest congratulations for the coming new year | and many happy returns of this day, | Truly yours Ferdinand Cohn

Footnotes

Cohn’s name is on CD’s presentation list for Movement in plants (Appendix IV).
Cohn’s inaugural dissertation Symbola ad seminis physiologiam (Contribution on the physiology of seeds; Cohn 1847) was a study of germination in ripe and unripe seeds. Theophil Ciesielski, a student of Cohn’s, had published on tip sensitivity in roots and radicles in Cohn’s journal, Beiträge zur Biologie der Pflanzen (Ciesielski 1872).
In Movement in plants, p. 99, CD had stated, ‘Circumnutation depends on one side of an organ growing quickest (probably preceded by increased turgescence), and then another side, generally almost the opposite one, growing quickest’.
CD had argued that curvature of cotyledons when exposed to light showed that light acted more as a stimulus, similar to the effect on the nervous system of animals, and not in a direct manner on the cell or cell-walls that contracted or expanded (Movement in plants, p. 461). He also discussed hygroscopic movements (ibid., p. 489), but did not mention contractile properties of protoplasm.
CD had described the circumnutation of an Oscillaria (at that time, classified as a thallogen or plant with no differentiation such as algae, but now considered to be a form of cyanobacteria; see Movement in plants, p. 259).

Bibliography

Ciesielski, Theophil. 1872. Untersuchungen über die Abwärtskrümmung der Wurzel. Beiträge zur Biologie der Pflanzen 1 (1870–5) Heft 2: 1–30.

Cohn, Ferdinand Julius. 1847. Symbola ad seminis physiologiam. Dissertation. Berlin: Günther.

Movement in plants: The power of movement in plants. By Charles Darwin. Assisted by Francis Darwin. London: John Murray. 1880.

Summary

Response to Movement in plants. Setting out to confirm CD’s experiments. Believes plant cell motion, like that of animals, depends on protoplasm more than water.

Letter details

Letter no.
DCP-LETT-12940
From
Ferdinand Julius Cohn
To
Charles Robert Darwin
Sent from
Breslau
Source of text
DAR 161: 206
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 12940,” accessed on 29 March 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-12940.xml

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