16 STRUCTURE AND PROPERTIES 



exposed to the air, with the single exception of 

 the stigma, is covered by this membrane, which 

 may generally be separated from the rest of the 

 tissue, and is seen under the microscope to be 

 formed of a range of flattened cells, distinct 

 from those of the Parenchyma. 



7. Stomata, or Pores, are exceedingly mi- 

 nute oval-shaped orifices, capable of expansion 

 and contraction, which are easily visible with 

 the assistance of the microscope on the cuticle 

 of the herbaceous surfaces of plants. They 

 exist more or less in all the leafy surfaces of 

 vascular plants, but are wanting in all roots, in 

 old stems, in fleshy fruits, and in all the organs 



coal must have been formed from resinous woods, even 

 though the remains of such were very scanty and im- 

 perfect. Now on applying the microscope to transpa- 

 rent sections of such fragments of coal as most distinctly 

 exhibit the fibrous structure it is seen that they present 

 the character which has been described, as peculiar to 

 the resinous woods the glandular form of woody fibre, 

 as it has been technically termed, and hence it is estab- 

 lished beyond doubt that the immense masses of coal 

 which now contribute so much in every way to the com- 

 fort and social improvement of the human race, are but 

 the remains of vast forests, probably the growth of many 

 successive centuries, which chiefly, if not entirely, con- 

 sisted of trees of the Pine and Fir kind." (Carpenter's 

 Veget. Physiology, pp. 65, 66. 



