A PIECE OF COAL. 



617 



amount of labor that can hardly be appreciated, but with results as 

 certain as if the actual development had been watched in the living 

 plant. 



The plants, themselves, on which this old coal-producing fruit 

 was borne, and whose carbonized stems and leaves lie heaped up and 

 mingled with the spores, have some lessons of interest for the student 

 of world-history. One of the best known of these plants has been 

 called Lepidodendron, or scale-tree, on account of the beautiful scale- 

 like markings impressed upon the bark (Figs. 1 and 2). These mark- 

 ings^ diamond-shaped and arranged in close-set spiral lines around 

 the stem are scars left by the falling leaves. Elaborately sculptured 

 stems are found in all our coal-measures, often with dimensions indi- 

 cating trees three to five feet in diameter, and seventy to a hundred feet 

 in height. Such trees, judging from their abundance and world-wide 

 distribution, must have been conspicuous objects in all the forest-cov- 

 ered swamps of the coal age. Conceive, if you can, of tall, rigid 

 trunks, ornamented with delightful patterns of inimitable sculpture- 

 work, rising to a height of thirty or forty feet and these dividing into 

 two equal clumsy branches ; then let each of these divide again and 

 redivide until a number though not a very great number of smaller 

 branches are produced ; then clothe each of the branches with a bris- 

 tling array of thick-set, lance-like leaves ; let each branch terminate in 

 a club-shaj^ed cone or fruit from which multitudes of resinous- spores, 

 at the proper seasons, came showering down, filling the air with clouds 

 of dust for days and weeks together, and sifting in among the roots of 

 all the dense undergrowth with which the coal-marsh is covered and, 

 having drawn this mental picture fairly, you will have some idea, per- 

 haps, of a Lepidodendron (Fig. 3). 



But, if we would award credit where credit is due, we must in all 

 fairness acknowledge the preeminent importance of another group of 



Fig. 9. Ideal Section of a Sigillaria-Stem : a. pith; b, woody cylinder; c, inner bark; d, 

 riud ; e, bases of leaves ; /, vascular thread running to the leaves ; g, medullary rays. 



plants to which we are indebted for by far the largest share of the coal. 

 These plants outnumbered the Lepidodendrons in all the swamps ; like 

 Lepidodendrons, they rose to the dignity of great trees ; the trunks 

 were composed of firmer and more densely packed woody tissue ; the 

 bark was thick and rich in bituminous matter, and in some of them it 



