228 Vegetable Tissue 



wise, its color is always caused by matter contained within it. 

 If a thin slice of elder be examined with a microscope, it will be 

 found to have a sort of honeycomb appearance, fig. 1, as if there 

 were a number of hexagonal cavities separated by partitions. 

 These are destitute of all perforations or visible pores, so that each, 

 as far as can be seen, is completely closed up from its neighbor; 

 although, as they have the power of filtering fluids with rapidity, 

 it is certain they must abound in invisible pores, and that they 

 are not impermeable, as if they were made of glass. Different 

 opinions, however, are entertained upon this subject, and we have 

 caused the supposed communicating pores or slits to be drawn 

 in the cells on the plate, as delineated by those who think they 

 have observed them. It may be observed that cellules often con- 

 tain air bubbles, which appear to have no direct means of escape, 

 and that the limits of color are often very accurately defined in 

 petals, as for instance in the stripes of tulips and carnations, 

 which could not be the case if cellular tissue were perforated by 

 such holes as have been described, for then all colors would 

 necessarily run together. The brilliant colors of vegetable mat- 

 ter, the white, blue, yellow, scarlet, and other hues of the corolla, 

 and the green of the bark and leaves, is not owing to any differ- 

 ence in the color of the cellules, but to coloring matter of different 

 kinds which they contain. In the stem of the Impatiens Bal- 

 samina, a single cell is frequently red in the midst of others that 

 are colorless. Examine the red cellule, and you will find it filled 

 with a coloring matter of which the rest are destitute. The bright 

 satiny appearance of many richly colored flowers depends upon 

 the colorless quality of the tissue. Thus, in Thysanotus Fasci- 

 cularis, the flowers of which are of a deep brilliant violet, with a 

 remarkable satiny lustre, that appearance will be found to arise 

 from each particular cellule containing a single drop of colored 

 fluid which gleams through the white shining membrane of the 

 cellules, and produces the flickering lustre that is perceived. 

 The coloring matter is frequently fluid, but is in the leaves and 

 other parts more frequently composed of granules of various 

 sizes ; this is particularly the case in all green parts, in which 

 the granules lie amongst greenish liquid, which, as they grow 

 older, dries up, whilst the granules themselves gradually change 

 to olive green, and finally to brown. The cellules develope 

 in some cases with great rapidity. The Supinus Polyphillis 



