The sun. [volume] (New York [N.Y.]) 1916-1920, 1919-05-04

itself owes most Of its brilliancy to
the same cause.
A question now arises which re-
quires careful consideration. The blue
cornfiower (Centdured cydnts) con-
tains the same chemical substance as
a purple pehrgonium. How can the
same anthocyanin give so entirely
different an external appearance7 And
how can only two kinds OF pigment
produce oil the profusion Of color to
DO seen in the garden? A considera-
ton OF the numerous factors detailed
below which can modify the color of a
pigment may indicate the answer to
both these questions.
(a) In the first place the nature of
the surface, usually called the cpl
dermis (see figure 81. of the petals has
profound effect upon the color shade.
The surface wall may be drawn up
Into little excrescences or pimples
(see figure 8. which represents a thin
transverse section through a velvety
petal. U. e. denotes the upper sur
face epidermis. and !. e. .he lower.
The shading is. artificial. and denotes
that these cells contain anthocyanin
dissolved in the cell sap). They are
usually called papille. and may &C.
casionally be prolonged into hairs. The
| combined effect of this roughened sur
face is to give the wonderful velvety
bloom so beautiful in many pansies
Viola tricolor). On the other hand.
the surface may be quite smooth and
fat. This gives the flower shiny
appearance, as is to be seen in the
hollyhock (Althded rosed). Very little
is known about the effect OF surface
color in ordinary objects, and the de-
gree to which 1t may alter the hue
| of flowers Is perhaps more considerable
than might be imagined. In orchids, for
| Instance, the structure Of the surface
sometimes attains an extraordinary
elaboration which has no doubt a cor
respondingly strong effect on the
shade. 1t may incidentally be remarked
that the marvellous purple bloom to
be seen on grapes, plums and many
other fruits Is nothing more than an
| exceedingly thin film of wax which
is excreted by the fruit and deposited
on the surface; the purple color it.
self, of course, is due to an anthocya-
rim.
(O) Among other structural condi.
tons may be mentioned the size, shape
and position Of the intercellular
spaces which have been mentioned as
the chief cause of whiteness. 1t is
clear that the presence of numerous
air spaces capable of rejecting white
light would tend to dilute the color
and make 1t paler especially IL they
lay In or above the layer of cells
which contain the principal pigment
that Is to say, a purple pigment NIGH,
he modified to any shade of lilac or
mauve. No doubt the shape and ar
rangement of such spaces with re-
gard to the other cells would furthe,
modify the final hue.
tc) The actual depth of the lave,
which contains the anthocyanins dis.
solved In their cell sap, as we'll as the
position of the layer within the petal
would affect the shade Of the color. As
a rule the anthocyanins are confined
to the outside layer of the cells, con-
tiguous to the air as is shown in the
Illustration (see figure 81. The cells
In the centre of the petal are gen.
orally free from anthocyanin. In the
case of the Oriental hyacinth (Hvdcin.
thus orfentdlis) the pigment is present
in the layer below the epidermis, the
latter being free from color. This gives