SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 781 



EXPLANATION OF PLATES. 



(All the figures are from untouched photographs.) 



Rhynia Gwynne-Vaughani, Kidston and Lang. 



Plate I. 

 Fi". 1. Vertical surface of a block from the chert band (E 10 of section on page 762), etched with 

 hydrofluoric acid to render the plant-remains more distinct. The dark layers s, s and s, s are silicious 

 sandstone with carbonaceous matter. From s, s to the base of the block and between s, s and s, s are two 

 layers of the silicified peat (P 1, P 2) composed of the remains of Rhynia Gwynne-Vaughani. The structure 

 of some of the larger stems is clearly shown, especially in the lower layer of peat. Natural size. (No. 5282.) 



Plate II. 



Fi<*. 2. Portion of the vertical surface of a block of the Rhynie chert which had been weathered 

 naturally. The rounded stems of Rhynia stand in low relief from the surface. Up to the level a-a, 

 which marks an original land surface, the stems lie horizontally in the silicified peat, but above this level 

 they are seen to become vertical. Natural size. 



Fi<*. 3. Portion of the horizontal surface of another block of the Rhynie chert showing the crowded 

 stems of Rhynia flattened down and compressed. Natural size. (No. 5283.) 



Fi<*. 4. A small portion of fig. 3 enlarged. At a and at other places the narrow ribbon-shaped com- 

 pressed stems show a raised median line marking the position of the stele. x 2. (No. 5283.) 



Fig. 5. A loose block of the Rhynie chert, etched with hydrofluoric acid and viewed from the side. The 

 lower portion up to the level of the old land surface a, a shows remains of Rhynia lying in all directions 

 in the silicified peat. From this level to the summit of the block the tapering aerial stems can be followed 

 bending over to the right. Natural size. 



Plate III. 



Fig. 6. Small stem exposed on a fractured surface of the chert showing the rounded form of the stem 

 and the epidermal cells which in this case have no median line. x 14. (No. 5286.) 



Fig. 7. Similar specimen showing a number of the small projections or bulges. The epidermal cells 

 in this and the following figure have the median ridge. x 14. (No. 5284.) 



Fig. 8. Hollow impression from which the stem has been removed showing the epidermis and three of 

 the small projections, x 14. (No. 5285.) 



Fig. 9. Portion of a vertical section through the peat. The stems in the lower part are more 

 compressed and decayed, while those above are uncompressed and separated more widely by interstitial 

 matter, x 5£. (Slide No. 2410.) 



Fig. 10. Portion of a similar vertical section through the silicified peat showing still more marked 

 decay and crushing of the stems at a and b. x 5|-. (Slide No. 2388.) 



Figs. 11-12. Enlargements of portions of fig. 13, PI. IV. For description see explanation to fig. 13. 



Plate IV. 



Fig. 13. Portion of section through peat composed of much decayed stems in which three rhizomes are 

 shown in their natural position. On the downwardly directed sides of all the rhizomes the epidermis 

 and outer cortex show increased development, which in the case of the longitudinal section is seen to have 

 resulted in the formation of two definite rhizoid-bearing bulges, a and b. A portion of the bulge a is more 

 highly magnified in fig. 11, PI. Ill, and of the bulge b in fig. 12. These figures, and especially fig. 11, show 

 the origin of the bulge by increased growth and division of cells of the epidermis and outer cortex. 

 o.c, outer cortex; i.e., inner cortex. Fig. 13, x 14. Figs. 11-12, x 60. (Slide No. 2412.) 



Fig. 14. Transverse section of a rhizome attached to the peat by rhizoids (rh.), and sending up an aerial 

 stem. Close to the base of the latter at st. a stoma was recognised. x 20. (Slide No. 2396.) 



Fig. 15. Small rhizome preparing to branch, the xylem of the stele having divided. x 20. (Slide 

 No. 2396.) 



