ANATOMY OF PLANTS. 



209 



ment of the calyx, and as we also see it in the colouring of 

 the bractese : since most of these pass again, when treated 

 with alkalies, into the green hue. The red juice of many 

 blossoms becomes, by means of alkalies, first blue, then green, 

 and, lastly, yellow. The iron in the soil has also a consider- 

 able influence in changing the red colour of the Hi^drangea 

 into a blue. When, from all these facts, we conclude, that 

 the green colouring matter, as it passes into the corolla, frees 

 itself from its superfluous hydrogen and azote, and, in that 

 way, becomes more oxydized, we are supported in this con- 

 clusion by a variety of considerations ; not only by the before- 

 noticed change of colours by alkalies, but also by the solubility 

 of the colours of blossoms in water ; and more than all this, 

 by the frequent exhalation of azotic and hydrogen gas from 

 blossoms. 



328. 



It cannot be denied, however, that a multitude of diffi- 

 culties still remain, and that many hypotheses must yet be 

 adopted and rejected, before we can flatter ourselves that we 

 have come near the truth. 



Of the utmost consequence, in particular, is the great va- 

 riation of colour, of which the Hibiscus mutabilis, and Gladio- 

 lus versicolor^ afford the most striking examples, although 

 the fact is seen, in an inferior degree, in many other blossoms, 

 which, when they are first unfolded, are coloured by tints 

 diff'erent from those which they afterwards assume. It seems 

 that this variation of colour passes most frequently into the 

 red, because many white and blue flowers take this colour 

 in their later stages ; nay, in a few cases, the yellow colour, 

 as in the Medicago media Pers., passes into the violet. It 

 cannot well be denied, that a variation in the proportion of 

 oxygen lies at the foundation of this fact. 



329. 



The smell of blossoms is another remarkable property, the 

 explanation of which will be facilitated, at least, in some de- 

 gree, by what we have already said respecting colours. It 



O 



