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Airy, Hubert in correspondent 
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From:
Hubert Airy
To:
Charles Robert Darwin
Date:
[before 15] July 1872
Source of text:
DAR 159: 16
Summary:

Outlines his theory on the origin of existing orders of leaf arrangement. Believes spiral and whorled orders have evolved from a primitive distichous arrangement. These arrangements permit a compact bud form of small surface area that can withstand external changes in temperature, and in particular can tolerate frost.

Contributor:
Darwin Correspondence Project
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From:
Hubert Airy
To:
Charles Robert Darwin
Date:
16 July 1872
Source of text:
DAR 159: 17
Summary:

Thanks CD for reading his MS [8412] and for his suggestions.

Clarifies his statement on the contraction of the bud-axis: did not mean to imply that this contraction occurred in an individual’s life-time, rather that it was the effect, after the course of ages, of successive favourable modifications.

Believes the true theory of phyllotaxy will give a convincing illustration and proof of the theory of evolution.

Contributor:
Darwin Correspondence Project
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From:
Hubert Airy
To:
Charles Robert Darwin
Date:
20 July 1872
Source of text:
DAR 159: 18
Summary:

Discusses the significance of the node. Believes, with CD, that it has no independent importance but is merely the consequence of the presence of a leaf. Does not believe a distinction can be made between whorled and alternate leaf arrangements on the basis of the number of leaves springing from a node. The node, as the starting point of a leaf, is subject to any disarrangement which takes place among the leaves.

Contributor:
Darwin Correspondence Project
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From:
Hubert Airy
To:
Charles Robert Darwin
Date:
21 July 1872
Source of text:
DAR 159: 19
Summary:

Corrects a factual error in his previous letter [8418].

Sends specimens illustrative of the "nodal" question.

Contributor:
Darwin Correspondence Project
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From:
Hubert Airy
To:
Charles Robert Darwin
Date:
24 July 1872
Source of text:
DAR 159: 20
Summary:

Responds to CD’s comments on his MS on phyllotaxy.

The initial variation required by his theory would be a slight twist of the bud-axis; believes the frequent twisting of stems and branches renders such a variation possible.

Admits he placed too much emphasis on the importance of frost. He should have spoken more generally of "vicissitudes of climate".

Contributor:
Darwin Correspondence Project
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