From J. D. Hooker [c. 20 February 1878]1
The cotyledon of grasses is a puzzle. There are three theories.
1. That the scutellum is the cotyledon
2. That the upper part of the scutellum is the cotyledon
3. That the first growth from the uppermost plumule2 is the cotyledon & the scutellum is only a development of the axis (radicle).
According to A. Gray in annexed sketch of maize a = cotyledon b = plumule c = radicle.3
The objection to this theory is, That when b grows—the back of its first leaf is dos a dos to a
Wherefore Sachs says that a cannot be cotyledon for if it were b would face it.4
Van Tieghem gets over the difficulty by supposing b. to be the ligule of the undeveloped plumule of the cotyledon a—which is a wriggle worthy of yourself!5
Sachs of course considers b to be the cotyledon.
G Henslow wriggles out of the difficulty by supposing the 2d. cotyledon of all monocots to be suppressed, & assuming that the first plumular leaf of grasses faced the suppressed cotyledon.6
Footnotes
Bibliography
Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.
Gray, Asa. 1857a. First lessons in botany and vegetable physiology, illustrated by over 360 wood engravings, from original drawings, by Isaac Sprague. To which is added a copious glossary, or dictionary of botanical terms. New York: G. P. Putnam; Ivison & Phinney.
Rendle, Alfred Barton. 1904–25. The classification of flowering plants. Cambridge: Cambridge University Press.
Sachs, Julius. 1875a. Text-book of botany: morphological and physiological. Translated and annotated by Alfred W. Bennett, assisted by W. T. Thiselton-Dyer. Oxford: Clarendon Press.
Tieghem, Philippe van. 1872. Observations anatomiques sur le cotylédon des graminées. Annales des sciences naturelles (botanique) 5th ser. 15: 236–76.
Tillich, Hans-Jürgen. 2007. Seedling diversity and the homologies of seedling organs in the order Poales (monocotyledons). Annals of Botany 100: 1413–29.
Summary
Discusses the structure of grass embryos; states differing theories regarding which part of the seed corresponds to the cotyledon.
Letter details
- Letter no.
- DCP-LETT-11220
- From
- Joseph Dalton Hooker
- To
- Charles Robert Darwin
- Sent from
- unstated
- Source of text
- DAR 209.4: 432
- Physical description
- AL
Please cite as
Darwin Correspondence Project, “Letter no. 11220,” accessed on 29 March 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-11220.xml