PREPARATION OF VEGETABLE TISSUES. 443 



For a detailed examination of these very interesting discoveries, 

 we must refer the reader to excellent papers, published by Mr. Henfrey, 

 in the Annals of Natural History, and in the Transactions of the Lin- 

 nean Society of London, vol. xxi., part 2, 1853. 



To return from this digression upon ferns. The siliceous cuticle 

 from the stems of grasses exhibits the beautiful arrangement of 

 silica so constant in exogenous plants, all of which are very in- 

 teresting objects for polarised light : Equisetum, wheat, barley, oat 

 or rye straw, Malacca cane, bamboo, &c. Hairs are found prin- 

 cipally upon the under surface of leaves; they are best seen when 

 viewed as opaque objects. Good specimens may be obtained from 

 leaves of Deutzia, Anchusa tinctoria, Borago officinalis, Dolichos pru- 

 riens, &c. Pollen should be viewed by the dark-ground illuminator, 

 and with a magnifying power of 100 diameters. That of the Passion- 

 flower is curious, and if immersed in dilute sulphuric acid is seen to 

 open and disperse the grains. The pollen of the Datura Stramonium, if 

 placed on a slide, and a few drops of dilute acid added, will send forth a, 

 tube of some length ; the granular matter in the pollen may be seen to 

 pass along the tube until it is emptied. For these observations a half-inch 

 power is required. Remarkable forms of pollen are found in the follow- 

 ing plants : Anagallis arvensis, Fuchsia globosa, Convolvolus, Jasmine, 

 Lychnis, Penstemon, Polygonum orientale, Tulip, Marvel of Peru, &c. 



The following are amongst the most characteristic examples of 

 woody fibre : flax, hemp, China-grass, section of pine, yew, date-palm, 

 cedar- wood, cork, oak, mahogany, root of gooseberry, sycamore, furze, 

 apple, vine, cotton, lace-tree bark, &c. In the cotton-plant, the hairs 

 are attached to and envelop the seeds ; their fibres are readily distin- 

 guished from those of linen, wool, &c. : being tubular fibres of cellular 

 tissue, these tubes, from the thinness of their sides, collapse, and 

 appear like flat ribbons or bands, woven or interlaced together ; which 

 is a reason for cotton being preferred to linen (flax) in making lint for 

 surgical purposes. 



Thin sections of charred wood sometimes show structures not seen 

 in any other way. In fossil woods, after making thin sections, it is 

 necessary to grind them on a lapidary's wheel, and afterwards polish 

 them. In the ashes of coal a variety of vegetable structures may be 

 discovered ; which must be rendered transparent by immersion in Ca- 

 nada balsam. Stones and shells of nuts are prepared in the same 

 way ; or we may grind them between a piece of cork and boxwood, 

 with fine emery-powder, as we should sections of bone. 



Sections of woods, if cut from hard woods, containing gum, resin, 



