VegetaUe PJiysiohgy. 409 



ceil-contents. Among these are the dissolved gases, carbonic 

 acid, oxygen, kc, mineral salts, salts of ammonia, &c. The 

 compounds of mineral bases with organic acids form a special 

 class of products, some of them occurring probably in most of 

 the higher plants in particular stages of growth. Their presence 

 has been chiefly noticed, and their relations to vegetative life 

 examined, in the cases where they exist in especial abundance, in 

 soluble (malates, nitrates, oxalates, &:c.) or insoluble. (oxalate ot 

 lime) conditions. The oxalate of lime occurs in great quantity 

 in a crystalline form in certain plants. The study of these com- 

 pounds in reference to vegetable life lies at present wholly in the 

 province of the chemist. 



The colouring matters of plants (exclusive of chlorophyll) are 

 at present ver}' imperfectly known as regards their chemical 

 relations to each other and to the other substances met with 

 in cells. Their mode of origin is, anatomically, similar to that 

 of the watery cell-sap in colourless cells, as described in a 

 former page (388), with the difference, that in the excavations 

 or " vacuoles " formed in the viscid protoplasm is produced a 

 coloured watery fluid, usually clear and transparent. As the 

 young colour-cell expands, the separate accumulations coalesce 

 in the central cavity of the cell : but the entire collection is 

 enclosed by the albuminous layer lining the cellulose wall, 

 through which it never passes, although a watery juice, during 

 the life of the cell. We mav very often observe two adjacent 

 cells with watery fluids of different colours, which, in the natural 

 state, do not intermix, although separated but by the delicate 

 cell-walls. When such cells are placed in a solution contracting 

 the primordial utricle, the latter shrinks up a little, and then 

 mostly bursts and emits the coloured watery fluid which exudes 

 through the cellulose membrane. Not unfrequently granular 

 bodies occur in the watery fluids of colour-cells ; these have not 

 been properly examined. 



The colour-cells of petals and other organs of flowers lie in 

 one or more layers immediately subjacent to the epidermal layer 

 of cells. The peculiar colours of the leaves of certain plants — 

 as of red-cabbage, beet, &c. — arise from the sub-epidermal layer 

 of cells being filled with a colouring fluid, like that of petals, 

 instead of containing chlorophyll as usual. The chlorophyll of 

 these plants lies in the deep middle region of the leaves, and is 

 screened by the interposed red cells, to which it imparts a bluish, 

 or greenish tint. In the red cabbage the ribs and veins of the 

 leaves have brighter red tints because there is no subjacent chlo- 

 rophyll in those parts, which are white in the green cabbage. 

 The red and the distinct yellow and orange hues which many 

 green leaves assume in autumn, ovvc their tints, in the first in- 



