CHAP. V. BRACTS AND FLORAL ENVELOPES. 
275 
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 ; 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 that of 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 de- 
hiscence 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 
conditions 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 
flowering are the same: the phenomena are in both cases 
also very similar. 
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