22 Objects for the Microscope. 



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 

 purple and white flowers, one species much resembling a 

 gorgeous 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 

 like a weed, having pretty buff or pink-coloured flowers, 

 covered with glandular hairs. 



SPIRAL CELLS OF BALSAM. 



These are from the common Balsam of our garden, and 

 show the bundles of long cells made up of spiral fibre, 

 which often break and pass into annular fibre : you may 

 perceive some of these in detached rings. These cells con- 

 tain air, and are those which most resemble the trachea of 

 insects. Those of the Leek are also very remarkable, and 



