506 ORDER CONIFERS; NATURE OF COAL. 



the process of fertilisation is here as direct as it possibly can be. 

 The seed is remarkable for having, in many species, a sort of 

 verticil of cotyledons instead of two only ; but these arise in the 

 same manner as the two which we find in other Dicotyledonous 

 plants, and may be regarded in the same light as leaves which 

 present a corresponding sub-division (. 235). 



681. The Coniferse certainly present the nearest approach to 

 Cryptogamia, which we anywhere find in the class of Exogens. 

 Their organs of fructification are reduced to the simplest form 

 they can possess, whilst still maintaining the character which 

 distinguishes the reproductive process in Flowering-plants. 

 (. 432). In the mode of growth of their stems, they are clearly 

 Exogenous ; differing from other trees of that class in little, ex- 

 cept that they do not possess ducts, and that their woody fibre 

 is of large diameter, and possesses glandular dots (. 78). It is 

 extremely interesting to be able to prove, by examination of such 

 minute points of structure, the real nature of those vast deposites 

 of Coal, which have long been a source of perplexity to those 

 who interest themselves in inquiries into the history of our globe. 

 Although in most instances the structure of Coal has been so 

 much altered, by the combined agency of water, heat, and pres- 

 sure, that it cannot be clearly distinguished, pieces may not un- 

 frequently be found, in which it is very evident, when examined 

 with the Microscope. It is then seen to correspond with Coni- 

 ferous wood, both in the characters which have been just men- 

 tioned, and also in the presence of a number of little receptacles 

 for secretion, in which a fluid is contained. This fluid may be 

 separated by distillation at a temperature beneath that of boiling 

 water ; and it is found to be identical with Oil of Turpentine. 

 It has been supposed, from the abundance of these remains of 

 Pine forests, and from the absence, in the same deposites, of the 

 remains of wood belonging to higher tribes of Plants, whilst the 

 stems and leaves of Tree-ferns have been most perfectly pre- 

 served, that none of those higher tribes existed on the Earth's 

 surface at that period. This inference, however, must not be 

 relied on ; for it has been found, by placing pieces of various 

 kinds of wood, with Fern-leaves, and other Cryptogamic struc- 



