BITUMINOUS COALS 195 



the case today in the peat deposits, and hence are classed with the 

 attrition matter and will be discussed under the attritus. 



Cuticles. — -The outermost layer of tissues of all leaves, petioles, 

 green parts of young stems, twigs, fruit, and seeds of plants, consists 

 of tabular cells very closely united and uninterrupted except by 

 stomatal pores. This is the epidermis. In some plants it persists 

 with but little change ; in others it is thrown off sooner or later and 

 replaced by a layer of cork. Dehcate epidermis possesses thin 

 walls; but in a large number of plants with fleshy and tough leaves, 

 the walls are of considerable thickness. 



The exposed surface of all epidermal cells are covered with a 

 layer of cutin forming a continuous transparent film or membrane 

 over the entire surface of leaf or stem. This film is called the 

 cuticle. It is present on all leaves, pedicles, green or young stems, 

 twigs, fruits, berries, and sometimes persists on older stems and 

 branches. Often the cuticle is further covered with a waxy and 

 resinous matter. In some cases the amount of such substances is 

 large and assumes commercial importance, as in the wax palm 

 (Ceroxylon andicola) and the bayberry (Myrica cerifera). The 

 waxy coatings may be in the form of coherent layers or incrustations 

 upon the cuticle; in crowded vertical rods, sometimes of consider- 

 able length; in very short rods or rounded grains, very much 

 crowded on the leaves of some plants; or in minute grains or 

 minute needles. 



The cuticle is very resistant to putrifying organisms and per- 

 sists under peat-forming conditions after most of the underlying 

 tissues have been disorganized or have disappeared. Cuticles or 

 fragments of cuticles are always present in peat, occasionally in 

 large proportions. 



Cuticles in coal. — ^Similarly in coals a large amount of cuticular 

 matter and some cuticularized tissues have survived and are ever- 

 present constituents, often forming very appreciable proportions 

 of the dull coal (Fig. 16). 



In thin sections, under the microscope, the cuticles appear as 

 bright golden-yellow bands of considerable length but relatively 

 narrow. One edge is usually smooth while the other is usually saw- 

 edged. Frequently they are found in pairs \vith the same-edged 



