XIV.] LIVING MATTER AND ITS EFFECTS. 241 



But what kind of trees were these ancient inhabitants 

 of the coal-forests, and to what existing plants could they 

 claim kinship ? To answer this question it is necessary to 

 turn not to our forest trees, but to such lowly plants as the 

 club-moss or Lycopodiidin. It may seem almost absurd to 

 compare such different objects as these ; for the club-moss 

 is a weak herb, and even in the most favourable conditions 

 does not rise to a height of more than two or three feet, 

 while the lepidodendron must have been a gigantic tree, 

 certainly reaching, in some cases, to a height of a hundred 

 feet. Yet, in the form of their stems, and in the character 

 of their fructification, the resemblance between the two is so 

 striking, that the student is forced to admit that the club- 

 moss is but a miniature edition of the old lepidodendron. 

 But, though the ancient and the modern plants thus differ so 

 much in size, it is curious to note that their spores are of 

 nearly the same dimensions. ^ 



At first sight, it no doubt seems surprising that objects so 

 minute as the spores and spore cases of extinct plants allied 

 to the club-moss should form any considerable proportion 

 of those vast masses of coal which occur in beds several 

 feet in thickness, and extend over areas measured in miles. 

 Yet in this case, as in that of the diatoms, the enormous 

 numbers compensate for want of size in the individuals. 

 Clouds of yellow dust, consisting of spores, may be 

 shaken from a branch of club-moss ; and the spores of the 

 diminutive species still hving are so abundant that they 

 form an article of commerce. The druggist rolls his pills 



' In some of the living club-mosses there are two kinds of spore?, 

 one being much larger than the other. The larger are known as macro- 

 spores, whilst the smaller are called microspores. Prof. Williamson, of 

 Manchester, who has paid great attention to the structure of coal-plants, 

 lias made the important suggestion that the large bodies, termed 

 "sporangia" in the te.xt, are really macrospores. 



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