444 SUMMARY OF CURRENT RESEARCHES RELATING TO 



but still visible amylosomes, imbedded in a homogeneous watery matrix 

 which swells up easily. This matrix is coloured blue by iodine, but the 

 extreme minuteness of the amylosomes rendered it difficult to determine 

 whether this was tho case with them also. He was unable to detect in 

 the starch - grains the presence of any albuminous substance. The 

 amylosomes when isolated arc singly, but in their natural position 

 doubly refractive. 



Function of Tannin.* — Prof. W. Hillhouse states that in all its forms 

 tannin is characterized by a weak acid reaction and an easily recognizable 

 astringent taste. Although it is convenient to speak of the group under 

 a single name, it must be borne in mind that the term includes a con- 

 siderable series of bodies of slightly varying character, and our know- 

 ledge of which is still extremely limited. Most of them appear to 

 be glucosidcs of gallic acid, and to be capable of resolution into 

 gallic acid and glucose ; those which give the blue-black reaction 

 with ferric salts as a rule yield pyrogallol, while those which give 

 the iron-green reaction commonly yield pyrocatechin. As regards 

 the general chemistry of tannin, two conclusions may be drawn, viz. 

 (1) that tannin is richer in carbon and oxygen than are carbohydrates, 

 and (2) that either free, or in comparatively loose combination with it 

 in the vegetable tissues, is an uncertain percentage of glucose. The 

 author conducted his experiments upon the following lines: — (1) To 

 determine whether the quantity of tannin in stems diminishes pari passu 

 with the increase in the quantity of starch ; (2) whether in spring the 

 quantity of tannin increases as that of starch decreases ; (3) whether in 

 germination and in stems in spring tannin is used up when the quantity 

 of starch or other carbohydrate has reached a low point. 



The author's experiments point to the conclusion that tannin, once 

 formed, is not used up in the further processes of growth, except perhaps 

 in the formation of resin ; and in this the evidence completely coincides 

 with the non-transfer of tannin from falling leaves, and from the leaves 

 of evergreens in winter. The function of tannin may be in some way to 

 protect the dead or dying parts of the plants from diseases due to the 

 attacks of fungoid organisms ; putting this on one side, evidence does 

 not support the view that tannin acts as a food-material analogous to 

 starch, glucose, or oil. 



Formation of Oxalate of Lime in Leaves.f — Herr A. F. W. Schimper 

 has made a detailed examination of the mode of occurrence and forma- 

 tion of crystals of calcium oxalate in the leaves of plants. Only rarely, 

 as in some families of mosses and in most ferns and grasses, does 

 this salt appear to be entirely wanting in the cell-sap. When the 

 crystals take the form of raphides, they are fully formed in the young 

 leaves while still growing ; but in the far larger number of cases where 

 the crystals of calcium oxalate take some other form, the quantity is very 

 small in young leaves, gradually increasing with age. An exceedingly 

 good instance of this gradual increase with age is furnished by the 

 leaves of Acer Negundo. 



Distinguishing the crystals formed during growth as primary, and 

 those formed after growth has been completed as secondary, the primary 

 crystals are formed independently of light, while the formation of the 



* Midi. Natural., x. (1887) pp. 269-76, 305-9; xi. (1888) pp. 5-11, 32-5. 

 t Bot. Ztg., xlvi. (1888) pp. 65-9, 81-9, 97-107, 113-23, 129-39, 145-53. 



