96 VIEWS OF THE MICROSCOPIC WORLD. 



figure 146 a quarter section of the same is exhibited considerably magnified. ID 

 the magnified figure, the area A A B B indicates the space occupied by the 

 skin of the bark, while the bark, consisting of cellular tissue and vessels, is in- 

 cluded within the limits B B C C. The large circular spots interspersed through 

 the bark are the gum-vessels of the Wormwood, which are likewise seen in the 

 bark of the stalk. Radiating from the centre of the section, and dividing it into 

 symmetrical portions, three complete figures are seen, shaped like the sticks of 

 an ivory fan, traversing the wood and extending into the bark. These figures 

 terminate in the bark in clusters of vessels, through which flows a limpid fluid 

 or sap ; and within these clusters one or more gum-vessels exists. The rest of 

 the figure comprises the woody portion of the root, which consists of two parts ; 

 namely, the true wood E, forming the lower part of the radial figure just des- 

 cribed ; and the cellular tissue, D, interposed between them, and running from 

 the bark to the very centre of the root. Throughout the true wood, spiral ves- 

 sels are scattered which increase in size from the centre outward. A section 

 of the common thistle displays great beauty in the formation of the cavities 

 of the cellular tissue. The pith consists of cells of different sizes, those of 

 the largest kind being one hundred times greater than those in the Oak. 

 These cells are not spherical, but are angular cavities of a regular shape, the 

 sides of which are formed of fibres running, in most cases, horizontally and 

 winding in a circular manner out of one cell into another ; a single ring of fibre 

 passing into no less than six cells, and constituting a side in each. Large spiral 

 vessels are distributed throughout the woody part, which is separated into regu- 

 lar oval-shaped compartments by thick divisions of cellular tissue, that penetrate 

 far into the bark ; while two sets of vessels, the one filled with a milky and the 

 other with a limpid fluid, are arranged on the outer verge of the pith in a double 

 row of crescent-shaped clusters. 



In view of the facts just adduced, we see at once the high utility of the micros- 

 cope in revealing to us the true nature of the structure of bodies. Pores or 

 vacant spaces are found diffused through the mass of bodies to such an extent, 

 that porosity is one of the leading mechanical properties of matter ; but in the 

 denser bodies the pores cannot be distinguished by the naked eye. And the 

 microscope is needed to render them clearly visible. Beneath its revealing 

 glasses, substances which before appeared solid, are now seen, perforated with 

 innumerable cells, which in the case of woods, occupy, for the most part, more 

 space than their intersecting sides ; and even the apparently solid sides of the 

 larger cells yield to the higher magnifying powers, and display a porous struc- 

 ture. 



FOSSIL WOODS AND PLANTS. 



Not only is the microscope eminently serviceable to the botanist, in revealing 

 the curious structures of living plants and their interior organization, but it is 

 highly useful to the geologist, who is enabled by its aid to read with the utmost 



