24 THE VEGETABLE KINGDOM. 



Spiral cells of Oncidium, 

 Spiral vessels of Collomia, 

 Spiral fibre from Balsam, 



Spiral cells of Sphagnum. 

 Scalariform vessels. 



They require some little explanation. We have already- 

 seen, in the examination of cuticles and newer-stems, that 

 plants are made up of cells containing various substances, 

 as starch, crystals, oil, or wax. These were for the nourish- 

 ment of the plant ; but here are cells which are supposed 

 to assist in the circulation of air and moisture throughout 

 the system. Some of them strikingly resemble the trachea 

 of insects, and seem to communicate with the stomata as 

 the trachea do with the spiracles. 



SPIRAL CELLS OF ONCIDIUM. 



These beautiful little cells are obtained by macerating the 

 pulp of those leaves' which contain them, separating them 

 with a fine sable brush, or mounted needle. The Oncidium 

 is an orchis, a native of Peru, Mexico, and the West In- 

 dian Islands ; cultivated in hot-houses in England. They 

 are curious and beautiful plants, with spotted yellow or pur- 

 ple and white flowers, one species much resembling a gor- 

 geous butterfly. In all these plants the spiral cells abound 

 immediately under the cuticle, and, viewed with polarized 

 light, they resemble coils of coloured wire. 



SPIRAL VESSELS OF COLLOMIA. 



These fibre-cells are in the cuticle of the seed, and the 

 examination of them is so easily made, that it is well worth 

 doing. The cells which contain the fibre are in this in- 

 stance so delicate, that a drop of water causes them to break, 

 and the coil unrolls, shooting forth in long tubes, with an 

 appearance of life as they spring across the field of sight. 

 To see this, take a seed of Collomia, and cutting off a very 

 small piece of its skin, place it with a drop of water on a 

 slide under the thin glass, when you will perceive the fibre 

 uncoiling in all directions. The Collomia is a native of 

 America, but naturalised in our gardens, where it grows 



