ARAUCARIA AND PINUS IN COAL FORMATION. 365 



1) and is best known in the Araucaria excelsa, or Norfolk 

 Island Pine. 



These discoveries are highly important, as they afford 

 examples among the earliest remains of vegetable life, of 

 identity in minute details of internal organization, between 

 the most ancient trees of the primeval forests of our globe, 

 and some of the largest living Coniferas.* 



The structure of Araucarias alone has been as yet iden- 



• The transverse section of any coniferous wood in addition to the 

 radiating and concentric lines represented PI. 56a, Fig. 7, exhibits under 

 the microscope a system of reticulations by which conifers are distin- 

 guishable from other plants. The form of these reticulations magnified 

 400 times is given in Pi. 56a, Figs. 2, 4, 6. These apertures are trans- 

 verse sections of the same vessels, which are seen in a longitudinal sec- 

 tion at Pi. 56a; Fig. 8, cut from the centre towards the bark, and parallel 

 to the medullary rays. These vessels exhibit a characteristic and beauti- 

 ful structure, whereby a distinction is marked between the true Pines 

 and Araucarias. In such a section the small and uniform longitudinal 

 vessels, (PI. 56a, Fig. 8) which constitute the woody fibre, present at in- 

 tervals a remarkable appearance of small, nearly circular figures disposed 

 in vertical rows (See Pi. 56a, Figs. 1, 3, 5.) These objects under the 

 name of glands or discs, are differently arranged in different species; they 

 are generally circulai', but sometimes elliptical, and when near each other, 

 become angular. Each of these discs has near its centre a smaller circular 

 areola. PI. 56a, Fig. 1, represents their appearance in the Pinus strobus of 

 North America. 



In some Conifers, the discs are in single rows; in others, in double as well 

 as single rows, e. g. in Pinus strobus, PI. 56a, Fig. 1. 



Throughout the entire ganus of the living Pines, when double rows of 

 discs occur in one vessel, the discs of both rows are placed side by side, 

 and never alternate, and the number of the rows of discs is never more than 

 two. 



In the Araucarias the groups of discs are an-anged in single, double, 

 triple and sometimes quadruple rows, see Pi. 56, Fig, 3. 5. They are much 

 smaller than those in the true Pines, scarcely half their size, and in the double 

 rows they always alternate with each other, and are sometimes circular, but 

 mostly polygonal. Mr. Nicol has counted a row of not less than fifty discs 

 in a length the twentieth part of an inch, the diameter of each disc not ex- 

 ceeding the thousandth part of an inch; but even the smallest of these are of 

 enormous size, when compared with the fibres of the partitions bounding 

 the vessels in which they occur. 



31* 



