MICROSCOPE IX THE GARDEN. 21 



cuticle, of cellular tissue ; but the inner layer, before 

 we come to the wood of the stem, is composed of 

 woody tissue. The cellular layer next the woody 

 one is often enveloped to a very great extent, and 

 then constitutes what we know by the name of 

 cork. The bark from which corks are made is 

 obtained from an oak-tree, which grows in the 

 Levant. If we make a very thin section of a cork, 

 its cellular structure can be easily made out. The 

 cells are almost cubical, and when submitted to the 

 action of a little solution of caustic potash, they 

 may frequently be seen to be slightly pitted 

 (Fig. 54, PI. 3). 



Many of the structures which are described above 

 may be seen in common coal ; thus proving most 

 satisfactorily that this substance has been formed 

 from a decayed vegetation (Figs. 55, 56, PL 3). 

 The examination of coal, however, is by no means 

 an easy task, and the hands and fingers may be 

 made very black, and the Microscope very dirty, 

 without any evident structure being made out. 

 Some kinds of coal are much better adapted for this 

 purpose than others. Sections may be made by 

 grinding, or coal may be submitted to the action of 

 nitric acid till it is sufficiently soft to be cut. The 

 amateur will not find it easy work to make sections 

 of coal ; but should he wish to try, he may fasten 

 a piece on to a slip of glass with Canada balsam, 

 and when it has become firmly fixed, he may rub 

 it down on a fine stone till it is sufficiently thin to 

 allow its structure to be seen under the Microscope. 

 Coal presents both vascular and cellular tissue. 

 The vascular tissue is, for the most part, of the 

 glandular woody kind ; thus leading to the inference 

 that the greater portion of the vegetation that 

 supplied the coal-beds belonged to the family of 

 the firs. 



