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Darwin Correspondence Project

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).

diagram

According to A. Gray in annexed sketch of maize a = cotyledon b = plumule c = radicle.3

diagram

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

The date is established by the relationship between this letter and the memorandum from George Henslow, [c. 20 February 1878].
In grasses, the plumule is the first shoot within the embryo.
See A. Gray 1857, p. 16.
For Julius Sachs’s views of the structures of grass seeds, see Sachs 1875, pp. 541–3.
See Tieghem 1872, pp. 265–7. Van Tieghem homologises the ligule of the vegetative leaf with the pileole (coleoptile) of the cotyledon, and views the scutellum, lobule (i.e. epiblast), and coleoptile as parts of the specialised cotyledon of grasses. CD and Hooker had a running joke in their correspondence about ‘wriggling’ in arguments; see, for example, Correspondence vol. 5, letter to J. D. Hooker, [3 November 1854].
See memorandum from George Henslow, [c. 20 February 1878]. On the disputed structures in the seeds of grasses, see also Rendle 1904–25, 1: 233–5. For a discussion of seedling organs in monocotyledons, see Tillich 2007.

Bibliography

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Tieghem, Philippe van. 1872. Observations anatomiques sur le cotylédon des graminées. Annales des sciences naturelles (botanique) 5th ser. 15: 236–76.

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

Please cite as

Darwin Correspondence Project, “Letter no. 11220,” accessed on 21 October 2021, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-11220.xml

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