FUNCTION.] SOURCE OF NECTAR. 509 



expand. In that plant, jnst before the opening of the flower, 

 the petals are folded up ; the glandular disc 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 

 disc 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 disc, 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 disc gradually dries up, and, in the end, the disc perishes 

 along with the other organs to which it appertained. If the 

 disc 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 fsecula, as the tubers of the Potato, Cyperus esculentus, &c. 

 This led Dunal to suspect that the young discs 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, subequently to their bursting, no 

 trace of fsecula could be discovered. Hence he inferred that 

 the action of the air upon the humid faecula of the disc had 

 the effect of converting it into a saccharine matter fit for the 

 nutrition of the pollen and young ovules ; just as the fsecula 

 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 



VOL. n. p 



