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 jhe 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 oi'gans 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, exlialing 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 w^hich 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, C}^erus 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 favoui*able; 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. 



T 2 



