WEST, ON PETALS OF FLOWERS. 23 
elevation is almost invariably greatest on the imner surface 
of the petals, and the descriptions here given, with only one 
exception, apply to such. Between the cuticles the tissue is 
generally stellate, in one or several layers. 
These elevations may be formed, either by general con- 
vexity of the outer cell-wall (Ranunculus aquatilis, fig. 1—iris, 
fig. 2), or dome-shaped (ten-week stock, fig. 3), or a partial 
elevation of the centre (featherfew, Pyrethrum parthenium, 
fig. 4), mammilate (geranium, fig. 5—orchis, fig. 6), awl- 
shaped, acute (sweet william, fig. 7—mimulus, calceolaria, 
&e.) On the outer surface of the tubular corolla of 
Comfrey, Symphytum officinale (fig. 8), they are very long, 
and intermixed with undoubted hairs. In the Cruciate they 
appear to be the coloured petalline hairs of Balfour. The 
most rudimentary condition of these elevations is that of a 
minute papilla, rising abruptly from the centre of every cell, 
or nearly so; a good example of this is seen in Gladiolus 
(fig. 9). That they are truly hairs in a rudimentary con- 
dition, the examination of an extensive series of instances 
will leave no doubt. On the lip of a brilliant little blue 
lobelia every gradation may be met with, from the slightest 
convexity of the cells to true hairs ;4, m. in length, and 
equally so on the same part in Antirrhinum majus. 'To these 
mammillate protuberances has been attributed the velvety 
appearance of the surface of petals; they form truly the 
“‘pile,”’ so to say, “of the velvet.” It seems probable, also, 
that from their convex form, they may act as lenses in 
magnifying the brillianecy of the coloured chlorophyll. 
Another way in which the richness of the hues of flowers is 
enhanced would, perhaps, scarcely suggest itself readily to 
any but an artist. I allude to the separation of the colour 
into regularly arranged symmetrical spots by the colourless 
cell-walls, thus obtaining what is technically called “ air ;” 
an effect that is rudely imitated by artists, according to the 
substance on which they work and the facilities which their 
materials may afford for its production. That this idea is 
not fanciful, may be readily seen by comparing an imitation 
oe 
Arie 
F 
Ig & 
Sap Wes. 
ple, 
CP 
8.905%: 
BASS 
So Bait 
KO 
Cyory 2 
CI FEL 
ez. 
; 
2S 
4, 
. he rr 
x 
g! 
BD 
2, 
p, 
©. 
Qe. 
on wood of the stippling of the miniature painter (fig. 1), 
who requires thus to produce the utmost degree of bright- 
ness which his colours will afford with fig. 2, a diagrammatic 
