CHAP. VII. 
BRACTS AND FLORAL ENVELOPES. 
331 
the petals are folded up; the glandular disk that lines the 
tube of the calyx is dry and scentless ; and its colour is at 
that time dull, like the petals at the same period. But, as 
soon as the atmospheric air comes in direct contact with 
these parts, the petals expand and turn out of the calyx, the 
disk enlarges, and the aspect of both organs is altered. Their 
compact tissue gradually acquires its full colour and velvety 
surface ; and the surface of the disk, which before was dry, 
becomes lubricated by a thick liquid, exhaling that smell of 
honey which is so well known. At this time the stamens 
perform their office. No sooner is that effected than they 
wither, the petals shrivel and fall away, the secretion from 
the disk gradually dries up, and, in the end, the disk perishes 
along with the other organs to which it appertained. If the 
disk of an Almond flower be broken before expansion, it will 
be seen that the fractured surface has the same appearance as 
those parts which in certain plants contain a large quantity 
of faecula, as the tubers of the Potato, Cyperus esculentus, &c. 
This led Dunal to suspect that the young disks also contained 
faecula: which he afterwards ascertained, by experiment, to 
be the fact in the spadix of Arum italicum before the dehis- 
cence of the anthers ; but, subsequently to their bursting, no 
trace of faecula could be discovered. Hence he inferred that 
the action of the air upon the humid faecula of the disk had 
the effect of converting it into a saccharine matter fit for the 
nutrition of the pollen and young ovules; just as the faecula 
of the albumen is converted in germination into nutritive 
matter for the support of the embryo. 
In support of this hypothesis, Dunal remarks that the con- 
ditions requisite for germination are analogous to those which 
cause the expansion of a flower. The latter opens only in 
a temperature above 32° Fahr., that of 10° to 30° centig. 
(50° to 86° Fahr.) being the most favourable; it requires 
a considerable supply of ascending sap, without the watery 
parts of which it cannot open ; and, thirdly, flowers, even 
in aquatic plants, will not develope in media deprived of 
oxygen. 
Thus the conditions required for germination and for 
