66 



HARDVVICKE'S SCIENCE-GOSSIP. 



curved, transparent, and spine-like, with ratber 

 blunt points, apparently hollow at the other extre- 

 mity, and attached to the centre of cells arranged 

 somewhat in a stellate manner, and larger than those 

 forming the general substance of the leaf. Interspersea 

 with these, but less abundant, are small recurved 

 hairs, about one-fifth the length of the others, in 

 shape resembling fish-hooks. They are commonest 

 on the younger leaves. The so-called "pellucid dots'' 

 of Loudon, which may be seen on the leaves by 

 holding them up to the light, wlien the leaves are 

 placed in water and their upper surface examined 

 with a i-iach objective, are resolved into seven or 

 eight rather large cells, radiating from the sides of 

 a centre cell, which appears raised slightly above 

 the surface of the leaf, so that the surrounding 

 cells appear to slope away from it. Below these, 

 and in the parenchyma of the leaf itself, is a large 

 single cell, within which is suspended a subglobular 

 or slightly pear-shaped mass with a papillated 

 surface, but with no clearly defined crystalline 

 structure. These bodies are known as Spliosraphides, 

 and have also been called " Crystoliths " by Conti- 

 nental writers ; they are sufiiciently large and hard 

 to be easily separated from the parenchyma of tlie 

 leaf when thin sections are made, or small portions 

 torn up under the microscope. When treated 

 with muriatic acid, they dissolve rapidly 'with 

 considerable ebullition, and when burnt are reduced 

 to a white powder ; there can be no doubt that they 

 are, therefore, chiefly composed of lime, and 

 probably in the form of carbonate. They differ from 

 the true raphides, so abundant iti many plants, by 

 being almost amorphous, though occasionally a 

 slight semicrystalline appearance may be detected 

 in small fragments if examined with a quarter 

 objective. Although not so often noticed as true 

 raphides, tliey are characteristic of many tribes of 

 British plants ; as the Caryophyllaceaj, Gerauiaceee, 

 Lythracese, Chenopodiacere, and especially the 

 Urticacese ; and it is thought by some botanists that 

 they afford a good diagnostic character for species. 

 In some exotic plants these splia>raphides occur of 

 considerable size, forming a weighty grit, and are 

 especially large and fine in the Prickly Pear and 

 others of the Cactus tribe. If we look to the use 

 of this curious and elaborate structure in the leaves 

 of plants, and ask what is its object in the 

 economy of nature, it is a question easier to ask 

 than to answer. Some suppose that raphides are 

 perhaps rather a disease than formations of natural 

 growth in plants ; but they are of too common an 

 occurrence and too universally distributed over the 

 whole tissue of certain species for this to be the case_ 

 In some instances they are doubtless useful as a medi- 

 cine, and the genuineness of sarsaparilla, guaiacum 

 and squills may be tested by the presence or absence 

 of raphides. It is probable, as Dr. Gulliver suggests, 

 that the large proportion of these crjstalline bodies. 



being compounded of phosphate or oxalate of lime 

 or some other compound of this earth, and remember- 

 ing the value of these substances in the growth and 

 nutrition of plants, that nature has estabhshed in 

 some plants a [storehouse or laboratory of such 

 calcareous salts, and that we may thus get a glimspe 

 of the utility of these crystals. 



Chemical Processes in Plants.— Professor 

 Emmerling has lately, with the object of extending 

 the slight knowledge we possess of the chemical 

 processes which occur in plants, set himself the task 

 of ascertaining the action of the plant-acids (oxalic, 

 tartaric, malic, &c.) on those mineral salts which 

 are of importance in the nourishment of plants. To 

 this end he has examined, in the first instance, the 

 behaviour of oxalic acid towards the nitrates of cal- 

 cium, potassium, and sodium ; having chosen this 

 case, because there is no doubt that plants in 

 general take up nitrates from the soil, and because it 

 is equally certain that oxalic acid is present in most 

 plants. The action between solutions of oxalic acid 

 and calcium nitrate was determined under all pos- 

 sible conditions, regard being paid to the influence 

 of time, of concentration, of an excess of the one 

 or the other reagent, and of the presence of other 

 salts. The reaction consists in the separation of 

 crystalline calcium oxalate and of free nitric acid. 

 The amount of oxalate precipitated depends on the 

 conditions of experiment ; it is less the greater the 

 dilution and the shorter the time of action. Even 

 when highly dilute solutions are employed, however, 

 the amount of precipitate is very considerable, and 

 if the action be continued sufiiciently long, almost 

 complete precipitation is effected, the formation of 

 a precipitate ceasing to take place only when the 

 solutions are enormously diluted. The separation 

 of oxalate is not only increased by an excess of cal- 

 cium nitrate, but also by an excess of oxalic acid : 

 nitric acid has a contrary action. Prom these re- 

 sults the author concludes that the plant-juices 

 necessarily contain free nitric acid. With regard to 

 the crystalline forr.i which the deposited calcium 

 oxalate takes, he finds that it is exactly that which 

 is of most common occurrence in plants ; the crys- 

 tals separate in mouoclinic prisms of theorthoclase 

 form, possessing an extraordinary tendency to form 

 twins, and frequently united in aggregates, such as 

 are often met with in plants, and known as " morn- 

 ing stars." Raphides were not observed. By 

 applying the method of difl'usiou, M. Emmerling 

 has also succeeded in establishing the fact, that the 

 nitrates of the akalies are partially decomposed by 

 oxalic acid in very dilute solution, with separation 

 of free nitric acid. Although, in his estimation, 

 there is no doubt of the separation of nitric acid in 

 the plant, he does not believe that it long remains 

 present as such, but that it is probably further 

 convertedj^by reduction into ammonia or hydroxy- 



