26 MICROSCOPIC ILLUSTRATIONS. 



reader only a general outline ; to enter upon any thing 

 like details would of necessity extend an introductory 

 chapter of this description far beyond its proper bounds. 

 I may, nevertheless, be permitted to make use of one 

 example by way of illustration. But how shall I select 

 one where the materials suited to construct it are so 

 superabundant, and where they all present so many 

 points of interest ? It will be readily admitted that this 

 is by no means an easy choice. I will limit my obser- 

 vations, however, to a single microscopic slider, and see 

 what instruction is derivable from it. Suppose this 

 slider to contain some sections of a recent or fossil wood ; 

 for instance, three specimens or shavings of such ex- 

 treme tenuity, that if they were exposed, they would be 

 wafted away on the slightest breeze. Let them be 

 weighed, and they will not exceed a grain. Hand them 

 to the chemist, and he can only prove to you that their 

 primary constituents are oxygen, hydrogen, carbon, ike. 

 and in so doing he will destroy them. What, then, does 

 an inspection of them under the microscope reveal ? It 

 will tell you, in the first place, whether they grew up, 

 like our forest trees, by yearly additions to the outside of 

 their woody centres, or by internal accessions, like most 

 of the. productions of the tropics. It will tell you 

 whether their leaves were veined or not whether their 

 embryos were dicotyledons or monocotyledons whether 

 the trees from which they were cut had branches or not 

 and, if they had, whether these were thick and sturdy, 

 like the boughs of the oak ; or thin and flexible, like the 



