EXPLANATION OF PLATE 57. 97 



Fig. 5. Longitudinal Sections of Araucaria excelsa, show- 

 ing polygonal disks, in double and triple rows, on the 

 surface of the longitudinal tubes. Some of the tubes 

 are without disks, as in all Coniferse. 



Fig. 6. Transverse Section of Araucaria excelsa. 



a. Portion of concentric annual layer. 



Fig. 7. Radiating and concentric structure of a branch 

 of Pinus, as seen by the naked eye in a transverse 

 section ; the microscopic reticulations are omitted 

 (See V. I. p. 365. Note.) 



a. a. Concentric annual layers, indicating periodical 

 growth. 



Fig. 8. Longitudinal Section of Pinus, showing the rela- 

 tive positions of the longitudinal vessels and medul- 

 lary rays. 



a, Longitudinal vessels, forming the woody fibres. 



b, Medullary rays. 



Plate 57. V. I. p. 371. 



Sections exhibiting the silicified remains of Coniferae and 

 Cycadeas, in their native bed, between the Portland and 

 Purbeck stone, on the coast of Dorsetshire. 



Fig. 1. Appearance of trunks and roots of large Coni- 

 ferous trees, and of trunks of Cycadites, in the black 

 earth, which formed the soil of an ancient Forest in 

 the Isle of Portland. (De la Beche.) 



Fig. 2. Remarkable concentric Ridges of Stone, around 

 the erect stump of a Fossil Tree in the Isle of Port- 

 land. See V. I. p. 372. Note. (Henslow.) 



Fig. 3. Inclined position of the petrified stumps of large 

 Coniferas, and of the bed of black mould and pebbles 

 in which they grew, near Lulworth Cove, on the 

 Coast of Dorset. (Buckland.) 



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