168 MISCELLANEOUS COMMUNICATIONS. 



trisj, the Ash, (Fraxinus exculsior), and others. The foliage of the Alder," 

 on the contrary, rarely hecomes yellow but falls green. That of the Oak 

 becomes not yellow but brown. The yellow foliage afterwards assumes the 

 same brown colour when it is dried after its fall. Various researches have 

 already been made on the yellow colour of the foliage. Macaire Prinsep 

 communicated the result of several experiments on the autumnal coloration 

 of the foliage ; and the general conclusion is, that the foliage in Autumn 

 ceases to evolve oxygen, but that it takes this gas from the air, that there is 

 then formed an acid which tinges the foliage at first yellow, then red, 

 and that this acid may be neutralized by an alkali, so that the foliage recovers 

 its yellow colour. Like Clamor Marquart, he regards these colorations as 

 modifications of one and the same colouring matter, which he terms chromule; 

 and he says that it is the cause of the ordinary yellow or red colour of the 

 petals. These results, Berzelius represents to be quite incorrect. Foliage 

 once tinged yellow never becomes green under any re-agent ; but foliage 

 which has become red resumes a green colour on the addition of potass, be- 

 cause its red colouring matter forms green combinations with its alkali. Leo- 

 pold Gmelin first directed attention to the difficulty with which the experi- 

 ments of Macaire Prinsep could lead to precise results. Guided by this 

 observation, Berzelius undertook some researches on the colour of the foliage 

 altered by the agency of the autumnal cold. These he performed chiefly on 

 the citron-yellow foliage of the common Pear tree ( ' Pyrus communis ) which 

 was put recently and at the moment at which it was collected in a bottle, 

 and completely covered with alcohol of 0.833, with which it was left in con- 

 tact for forty days. The alcohol acquired a yellow colour ; but the foliage 

 was still yellow, though paler than before. The alcohol was decanted and 

 the flask was kept for some time inverted. The foliage then acquired a 

 brown colour, wherever it was in contact with the air, while the sides of the 

 leaves which were in contact with the walls of the vessel, retained their 

 yellow tint. Alcohol was poured at several intervals on the leaves, and each 

 time was coloured yellow. At length the alcohol was made to boil, when it 

 acquired a colour a little yellowish, but it became gelatinous during cooling. 

 The cause of this gelatinous state is the presence of a fatty matter, pecu- 

 liar probably to the foliage examined which is obtained colourless after wash- 

 ing with cold alcohol, from new solutions and renewed washings. It pos- 

 sesses the following properties. In the dry state it is of a milky white, its 

 fragments similar to chalk. It becomes soft under pressure ; it is inodorous 

 and tasteless. It melts at 73°, and becomes concrete and turbid on cooling. 

 Insoluble in water, it requires 425 parts of cold alcohol to dissolve it. A sa- 

 turated solution at boiling heat is converted, on cooling, into a transparent 

 jelly like paste. Cold ether dissolves little of it, but more than alcohol. It 

 is insoluble in caustic potass. It passes without change to the dry distilla- 

 tion, if, during the process, air be excluded. The leaves maceraled as now 

 described, were now distilled to one-eighth ; and there was then deposited on 

 cooling, a granular substance, which presented a species of crystallization. 

 After the separation of this substance, the distillation was continued till 

 nothing was left but the water of the vegetation of the leaves. On this yel- 

 low brown liquor was then floating a yellow soft fatty substance, with an ap- 

 pearance identical to that of the grains containing the yellow colouring mat- 

 ter of the foliage. These grains presented to the microscope no trace of 



