TRANSACTIONS OF SECTION K. 819 
Hence the pigment most likely arises through enzymic action. Slight alkalinity 
hastens its appearance. Oxygen is also necessary for its formation. It is readily 
soluble in water and gives a fluorescent solution, purple to violet by transmitted 
and blood-red by reflected light. A trace of acid robs the solution of most of its 
colour. The original tint reappears on neutralisation. Alkali turns it bluer, and 
if strong changes it to green, eventually destroying it. Light does not alter it. 
All parts of the plant except the flower can produce the pigment. 
Such a reducing agent as stannous chloride decolorises an aqueous solution of 
the pigment. Micro-organisms can also readily bleach it, when oxygen is excluded. 
On allowing air to enter, the original colour at once returns. 
The whole phenomenon bears some resemblance to the way in which indigo 
arises in plant-tissues. The chromogen of Jacobinia is probably a glucoside. In 
the living cell this substance and its enzyme may be differently situated, perhaps 
one in the protoplasm and the other in the sap. On the destruction of the cell 
the two come in contact. ‘he first result is the formation of a colourless body. 
Then this through the oxygen of the air, possibly assisted by an oxidase, is changed 
into the pigment. 
This behaviour of Jacobinia is perhaps only a striking instance of a common 
feature of plant-juices, viz., their tendency to darken on exposure to the air. 
7. Saponarin (‘Soluble Starch’). By Guorcu Barger. 
Dissolved in the cell-sap of the leaf epidermis of a number of plants there 
occurs a substance which is coloured blue by a solution of iodine in potassium 
iodide. This so-called ‘soluble starch * was first observed in 1857. Sanio found 
it in the leaf epidermis of Gagea lutea, and Schenk in that of three species of 
Ornithogalum. Similar observations were afterwards made by Trécul, Nigeli, and 
Kraus. The last important paper was by the Swiss botanist Dufour, in 1886; he 
found the substance in about twenty different plants, and investigated its physio- 
logical importance. The first (and unpublished) attempt to isolate the substance 
was made by the late G. Clautriau. Later, when the author was his successor as 
assistant to Professor L. Errera at the Brussels Botanical Institute, the latter 
suggested a renewed investigation of the substance. 
Fairly large quantities of the chemically pure substance have been isolated 
from the leaves of Saponaria officinalis, L. It has accordingly been called 
Saponarin; it may or may not be identical with the ‘soluble starch’ of all the 
other plants. 
Saponarin is a glucoside; it crystallises in small needles, and its probable 
formula is C,,H,,O0,,, On hydrolysis it yields glucose and a substance which is 
closely related to the class of bodies known as flavones. 
Flavone derivatives are widely distributed in plants, either as such or combined 
with sugar, as glucosides. Their physiological function is doubtful ; perhaps they 
are merely waste products. 
For the detection of saponarin under the microscope the following reactions 
cau be applied to sections or to strips of the epidermis :— 
1, With iodine and potassium iodide the whole of the cell-sap is coloured 
uniformly blue or violet, and the substance which issues from injured cells pro- 
duces the same colour outside these cells. On warming, the colour disappears ; it 
reappears on cooling outside the cells. 
2. Dilute alkalis and alkaline carbonates, as well as strong hydrochloric or 
sulphuric acid, produce an intense golden-yellow colour, first inside the cells con- 
taining saponarin, and then outside, 
3. Ferric chlovide produces a reddish-brown colour in these cells ; sometimes 
the colour is green or violet, owing to the simultaneous presence of tannins. 
These micro-chemical reactions of saponarin were used in the investigation 
of its physiological importance, but no very definite results were arrived at. 
8G 2 
