274 M. Macaire Prinsep on the Cohuritig of the 



the fat and essential oils of the green matter, and the insolubili- 

 ty of the yellow resin in these same menstrua, and the action of 

 acids and alk'tilies. In fact, a prolonged abode, even in the 

 cold state, of the yellow resin in the alkaHes, brings it back to a 

 beautiful green colour, and the action of heat accelerates this 

 effect. It is then in all respects similar to the chlorophyle, and 

 becomes, Hke it, soluble in oils. On the other hand, all bodies 

 capable 'of yielding their oxygen, as acids, or the employment of 

 means which facilitate the combination of that gas, as the expo- 

 sure to the air of the alcoholic solution, heat, &c. make the 

 chlorophyle pass to the yellow or red colour ; so that the resin of 

 the leaves which have undergone the autumnal colouring, seems 

 to be nothing but gteen resin oxygenated, or having undergone 

 a kind of acidification. 



If a yellow leaf of any tree whatever is allowed to remain 

 some time in potash j it becomes of a beautiful green, without 

 experiencing any sensible alteration. Ammonia, and all the 

 alkalies, produce the same effect. On the other hand, when a 

 green leaf is left in an acid, it becomes yellow or red, and po- 

 tash restores the gi-een colour, &c. It were impossible to retain 

 the name of chlorophyle for a substance, which not only is not 

 always green, but which, as I have just said, exists elsewhere 

 than in the leaves^ and I had imagined the word phytochrome^ 

 when M. De Candolle, to whom I communicated these results, 

 informed me, that he had also felt the propriety of adopting a 

 new word, and had made choice of the term chromule, which I 

 shall employ in what remains of this memoir. 



If the reddened leaves of Rhus coriaria, or the pear-tree, are 

 treated with boiling alcohol of 40°, the liquor is coloured of a fine 

 blood red, and, by evaporation, deposits a resinous substance, 

 which becomes of a fine green by the action of alkalies. An acid, 

 in this case, restores the red colour. As the green chromule is fre- 

 quently seen to pass through the yellow hue, before arriving at 

 the red, we might naturally conclude that the latter is at a 

 higher degree of oxygenation. There results from these facts, 

 that the autumnal change in the colour of the chromule of the 

 leaves might easily be explained by the fixation of new doses of 

 oxygen, which would continue to be absorbed without being ex- 

 haled. This addition would produce successive alterations of 

 colour, without affecting any great change in the other proper- 



