The calyx may change in consistency and texture in proportion as the ovary, to which it adheres, changes into fruit. The fleshy pulpy substance of the apple, and, in general, of the fruits of the Pomaceæ, is simply an excessive development of the calicinal tube united all around the ovary, and recognisable in the pips, imprisoned, towards the centre, in horny lobes. In other plants, as the flower develops into fruit, the calyx becomes woody: such is the case with the Water Chestnut (_Trappa natans_). Finally, the calyx may even contribute to the dissemination of the seed. We may cite, as an example, a Brazilian species of Urticaceæ, which Saint-Hilaire named the _Elasticaria_. The fleshy and cylindrical parts of the calyx are curved inwards, and thus defend, as one might do with one's bended fingers, the young fruit until it is completely developed; as soon as the fruit is ripe, they spring up erect, and launch it to a distance. * * * * * _The Corolla._--If from the circumference we proceed to the centre of the flower, the calyx being the first, the _corolla_ will be its second envelope. If, on the contrary, we proceed from the centre to the circumference, the corolla will form the fourth whorl; the pistil (consisting of stigmata, stylus, and ovary) being the first; the nectariferous disc (often wanting) the second; and the stamens the third whorl. Remarkable for its varied tints, the corolla, to indifferent or ignorant eyes, seems the entire flower. A black or blackish colour is exceedingly rare. Out of 300 vegetable species which compose the flora of Central Europe, there are not six with blackish or even grayish flowers. No hypothesis has yet been put forward to explain this mark-worthy rarity. Species with a yellow corolla are the most numerous, forming more than a sixth of the European flora: then come, in their order of frequency, species with green, white, red, and blue flowers; the white increasing in number as we approach the Pole. Dividing the flora into twenty parts, we may ascribe to each colour, and its various tints, the following proportion:-- Yellow, 6.0 Green, 4.50 White, 4.0 Red, 3.50 Blue, 1.50 Black, 0.50 The analogy between the parts or _petals_ of the corolla and the leaf, is perhaps not quite so striking as between the leaf and the _sepals_ of the calyx. The phrase "rose-leaves" is an expression consecrated by immemorial usage. Why not prefer the term "corollary leaves or leaflets (_foliola_)" to that of petals?