760 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



substance is formed by passing atmospheric nitrogen (from which the 

 naturally intermixed oxygen has been extracted by heated copper) over 

 heated calcium carbide. The calcium cyanamide formed is a fine black 

 powder which decomposes with water into calcium carbonate and ammonia. 

 Experiments to ascertain its manurial value were made last year at 

 Rothamsted, and appear to show that it is slightly less valuable than 

 ammonium sulphate, but the experiments were not sufficient to give 

 decided information. This new substance seems to be especially valuable 

 in ensuring an ample continuous supply of combined nitrogen, because if 

 the output of other nitrogenous manures be restricted there is here a 

 means of keeping up the supply.— F. J. B. 



Calcium Oxalate, its Function in Plants. By M. Amar (Ann. Sc. 

 Nat., Bat. xix. pp. 197-291 ; 34 figs. ; 1904). — Crystals of calcium oxalate 

 are frequently found in the tissues of plants, yet their function is not 

 yet fully explained. From the review of existing literature in this paper, 

 two main theories stand out : (a) calcium oxalate may be a reserve supply 

 capable of being utilised if need be ; (b) it is an excretion by which an 

 injurious excess of oxalic acid is combined with calcium to form a 

 salt which is laid down as crystals. M. Amar's work suggests a third view. 

 He believes that the crystals are excreta, and that they are produced by the 

 neutralising of excess of calcium by means of oxalic acid. The plants 

 investigated are chiefly Caryophyllacece, and only the briefest review 

 can be given of the careful observations and experiments dealt with in 

 the three chapters. 



Chapter I. — Distribution of calcium oxalate crystals in the tissues of 

 plants. This is shown graphically in a series of figures. Roots and 

 rhizomes contain no crystals, or rarely a small amount. Stems show them 

 in the nodes, but they rapidly diminish upwards and downwards in the 

 internodes. Leaves always contain crystals, most in the blade, in tissues 

 round the veins ; also in somewhat less quantity in the leaf-stalk. 

 Axillary buds have many crystals, and these may also occur in the 

 carpels of flowers. 



Chapter II. — Is calcium oxalate a reserve or an excretion ? Plants 

 grown in soil till they had two, three, or four pairs of leaves were washed 

 and transferred to culture solutions containing no calcium. Other pairs 

 of leaves were developed, but these showed no crystals, either in the leaves 

 or stems developed in solutions without calcium. Nor did the plants 

 utilise the crystals formed during their growth in the soil. He therefore 

 concludes that calcium oxalate is not produced in the absence of calcium, 

 and that plants are unable to make use of calcium stored as oxalate. 



Chapter III. — Reason for the formation of calcium oxalate. Plants 

 were grown in a series of solutions in which the amount of calcium nitrate 

 was increased from nil to half a gram per litre. Assimilation was found to 

 increase with increased calcium, but when a certain limit was reached the 

 assimilation remained the same in spite of still further increase of 

 calcium. Crystals were not formed so long as the calcium in the solutions 

 remained below a certain limit, but above this the crystals increased more 

 or less equivalent to calcium supply. Calcium was necessary for the full 

 development of the plants up to a certain limit ; beyond this it was not 



