On the Colour of Leaves of Plants and their Autumnal Changes

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                                in which the young leaves in the spring are more or less red,
while the older leaves do not become so until the autumn, when 
they are about to fall.
Instances innumerable of red coloured leaves might be cited,
such a list however is not needed for this enquiry, but we may 
name in passing, that many of these belong to the genera 
rumeae, oxalis, salvia, amaranthus, Tradiscantia, Coleus,
[…]eranthus and though last, not least, brassica, including red and 
blue cabbages.
As a rule the red colour is most developed on the upper 
surface of the leaf and in some geraniums it begins in the 
thin edges; frequently both surfaces are coloured and occasionally 
it happens that the under surface is the most red and this 
is usually the case in the scimitar shaped leaves of the Blue Gum 
The red colour is often confined to a single layer of cells, in 
other cases it extends deeper and it sometimes involves the whole 
thickness of the leaf, comprising several layers of cells; these 
differences may be well seen in vertical sections of the leaves of 
many geraniums.
In the leaves, both young & old, of some geraniums, including 
the ivy-leafed varieties, a blackish, somewhat starred ring or 
band, is to be seen; this, owing to its dark colour stands out 
in marked contrast to the green of the rest of the leaf. I found 
to my surprise, <s>that <\s> when a thin section of the leaf, including 
a portion of the ring, was placed under the microscope, that 
it consisted of a layer of cells, filled with a ruby red colouring 
matter. The dark colour first seen was due no doubt to the density 
of the leaf being so great as not to permit the light to pass 
                            
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Manuscript details

Author
Arthur Hill Hassall
Reference
AP/69/1
Series
AP
Date
1892
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On the Colour of Leaves of Plants and their Autumnal Changes, 1892. From The Royal Society, AP/69/1

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