116 REPORT—1858. 
it was shown that immediately beneath the cuticle of leaves and petals is a layer of 
cells of small size, circular form, and variable colour, which is named the Refe. The 
central layer of leaves and petals, consisting of veins and larger cells, is called the 
Substance. In petals, the rete contains the colours, the substance being nearly or 
quite colourless. In leaves, the substance contains the great mass of green colour, 
the rete superadding the dark tints and marks. The present paper contains further 
observations by the author. 
1. Eight instances of leaves were examined during the autumnal change of tint. 
The change invariably begins in the rete or layer of cells immediately beneath the 
cuticle, whether upper or under ; and extends subsequently to the substance. ‘lhe 
rete is thus the principal seat of the brilliant autumnal tints of leaves. When the 
change begins on the upper surface of the leaf, it is first seen at the edges and in the 
intervenous spaces; when on the under surface, it is first observed in the centre, 
and in contact with the principal veins. 
2. The examination of numerous kinds of variegated leaves showed that yariega- 
tion is invariably thus produced: the young leaves are unfolded of one uniform tint ; 
then, when they are about half-grown, a patch of some other tint is developed on the 
upper surface, in the centre, and in contact with the principal veins. Variegation 
thus obeys an opposite law to that which regulates the autumnal tints and the 
accidental markings of leaves. It is, furthermore, of two different descriptions; in 
one, the edges are white and the centre green, the young leaves having been unfolded 
in a state of quasi-etiolation, and patches of green being afterwards developed in the 
centre; in the other, the edges are green and the centre yellow, the young leaves 
being green, and yellow patches being afterwards developed near the midrib. In 
both descriptions, in the green parts of the leaves, the rete, or layer of cells just sub- 
jacent to the cuticle, affords, as usual, the deepest green, the substance being of an 
ordinary green all through ; and in the light-coloured parts, the rete contains what- 
ever colour is presented, the substance being whitish all through. 
The patch thus developed, in one case yellow, in the other case green, begins to 
appear only when the leaf has attained some growth, and has consequently exercised 
its vital functions for some little time in contact with the atmospheric air. Then, 
not at the edges, like chance markings or the tints of incipient autumnal decay, but 
in the centre of the leaf, and therefore in contact with the principal veins, appears 
on the upper surface the patch, of either colour, and from those veins it spreads. 
Hence it is inferred, that the colouring matter in these patches, whether green or 
yellowish, is in a high and vigorous state of development, quite different from those 
tints which approximate towards decay. An accurate microscopical and chemical 
examination of the cells and their contents, both of rete and substance, in the light- 
coloured portions of variegated leaves, as contrasted with the green parts, is a 
desideratum. 
3. Of the ordinary tints and markings of leaves, eight special instances were 
examined ; proving that the substance is of a green colour which is very nearly uni- 
form in all leaves, and that the rete is the seat of the extra tints and markings. In 
regard to the veins and surfaces, these extra colours are invariably in one of two 
situations ; either in contact with the principal veins, and in such case most con- 
spicuous on the under surface of the leaf; or else quite away from the veins, occu- 
pying the intervenous spaces and edges of the leaf, and then mostly seen upon the 
upper surface. They thus obey the same law as the autumnal tints, and are probably 
of similar nature ; contrasting remarkably with the law above stated which regulates 
variegation. 
4. Numerous specimens of petals were examined, showing the absence of colour 
in the cuticle and substance, and the localization of the brilliant colours in the cells 
lying just beneath the cuticle, here called the rete. The most highly coloured cells 
are generally the smallest, always lie densely packed together, and are commonly 
roundish, sometimes elongated. 
5. The anomalous organs in half-double flowers, partly stamen and partly petal, 
suggested to the author that the pollen seemed to take the place of the coloured cells 
of the rete ; and that the cells of the rete in leaves and petals, became, in stamens, 
the pollen-grains. Sundry specimens were therefore examined, to ascertain how far 
the shape and size of the pollen-grains bore any relation to those of the cells in the 
