486 ARAUCARIA AND PINUS I!^ COAL FORMATION. 
trees of the primeval forests of our globe, and 
some of the largest living Coniferae.* 
The structure of Araucarias alone has been as 
yet identified in trees from the Carboniferous 
series of Britain. | That of ordinary Pines oc- 
*' The transverse section of any coniferous wood in addition 
to the radiating and concentric lines represented PI. 56^y Fig. 7, 
exhibits under the microscope a system of reticulations by which 
Coniferse are distinguishable from other plants. The form of 
these reticulations magnified 400 times is given in PI. 56^, Figs. 
2, 4, 6. These apertures are transverse sections of the same 
vessels, ^vhich are seen in a longitudinal section at PI. 56^, Fig. 
8, cut from the centre towards the bark, and parallel to the me- 
dullary rays. These vessels exhibit a characteristic and beautiful 
structure, whereby a distinction is marked between true Pines 
and Araucarias. In such a section the small and uniform longi- 
tudinal vessels, (PI. 56^, Fig. 8) which constitute the woody fibre, 
present at intervals a remarkable appearance of small, nearly 
circular figures disposed in vertical rows (See PI. 56*, Figs. I , 
3, 5). These objects under the name of glands or discs, are dif- 
ferently arranged in different species ; they are generally circular, 
but sometimes elliptical, and when near each other, become an- 
gular. Each of these discs has near its centre a smaller circular 
areola. PI. 56^, Fig. 1, represents their appearance in thePinus 
strobus of North America. 
In some Coniferte, the discs are in single rows; in others, in 
double as well as single rows, e. g. in Pinus strobus, PI. 56^, 
Fig. 1. 
Throughout the entire genus of 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 arranged 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 witli 
