rs of the typical form (Carriere).
This circumstance, however, is not of universal occurrence.

For further particulars on this interesting subject the reader is
referred to Darwin's 'Variation of Animals and Plants,' i, p. 373, where
numerous references are given, and wherein certain well-known and highly
remarkable instances, such as the _Cytisus Adami_, the trifacial orange,
&c., are discussed.

FOOTNOTES:

[366] 'Nature-printed Ferns,' 8vo edition, vol. ii, p. 197.

[367] 'Gard. Chron.,' 1845. p. 790.

[368] 'A New Arrangement of Phaenog. Plants,' p. 36.

[369] 'Bull. Soc. Bot. France,' 1856, t. iii, p. 569.

[370] The reader will find an abstract of Mr. Darwin's views in his work
on the 'Variation of Animals and Plants,' vol. ii, p. 181.

[371] Loc. cit., i, 336.

CHAPTER III.

ALTERATIONS OF COLOUR.[372]

Changes in the colour of the several organs of plants are more often
either pathological or the result of variation than of malformation
properly so called.

Alterations in colour arise from a diminished or an increased amount of
colouring matter, or from an unusual distribution of the solid or fluid
matters on which the colour depends. The superposition of cells
containing colouring material of different tints produces naturally a
very different set of hues from those which are manifested when the
colours are not blended. Referring the reader to the ordinary text-books
on vegetable physiology and chemistry for details as to the nature and
disposition of colouring materials in plants under natural
circumstances, it will only be necessary to cite a few instances of
deviation from the general colour of plants or their organs.

=Albinism.=--This change is due to the deficient formation of green
colouring matter or chlorophyll, and is more a pathological condition
than a deformity.

It seems necessary to draw a distinction between this state and ordinary
blanching or etiolation. In the former case chlorophyll seems never to
be formed in the affected parts, even if they be exposed to light, while
an etiolated organ, when placed under favorable circumstances, speedily
assumes a green colour. In _Richardia aethiopica_ one or more leaves
become occasionally as white as the spathe is usually.

=Virescence.=--Engelmann[373] pointed out that, so far as flowers were
concerned, there are two ways in which they assume a green colour,
either by a simple development of chlorophyll in place of the colou