772 DE R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 



In fig. 55 several small bulges are present around the stem, only one of which 

 has given rise to a branch. The branch in fig. 56 is itself branching. These 

 adventitious branches appear to have arisen from all regions of the stem. 



The particular example shown in fig. 58 is from a stem about 4 inches above 

 the ground, in the block shown on PI. II, fig. 5. 



Some of the branches had a fairly wide base of attachment (PI. VIII, figs. 56- 

 59, 61), while others widen out from a very narrow attachment (fig. 60). All 

 intermediate forms are found. The adventitious branches appear to have been 

 readily detached. In fig. 55 this separation of the branch has almost taken place. 

 Specimens with a very narrow stalk-like base of attachment have been met with 

 free in the peat, a good example being shown on PL X, fig. 72. This branch widens 

 rapidly but has not developed a stele. The distribution in the peat of such 

 detached branches suggests that new plants started from them, and that this was 

 an important method of vegetatively propagating the plant. 



Doubtless, as the branch grew on, a stele was differentiated in it, but small 

 cylindrical stems of various diameters without any indication of a stele have been 

 frequently met with (PI. X, fig. 73). Another example is shown in fig. 60, lying ' 

 beside the attached branch, which itself has no indication of a stele. 



The scar left by the separation of a branch often became the seat of degenerative 

 changes. Its position is then marked by a small black patch of dead tissue. The 

 adjoining cells had frequently elongated at right angles to this, the wound-reaction 

 showing that the separation of the branch had occurred during the life of the plant. 



The foregoing description of the vegetative organs of Rhynia Gwynne-Vaughani 

 has been based upon the best-preserved specimens. We may add a remark on some 

 results of less perfect preservation in producing a different structural appearance, 

 especially in the region of the stele. The fairly large stem represented in PI. X, 

 fig. 75, shows the commencement of the decay of the epidermis and of the inner 

 cortex. When this is more advanced it leads to the complete disappearance of the 

 inner cortex, only the stele and the thin cylinder of the outer cortex being preserved. 

 A further change affecting the stele has been observed in numerous examples of 

 partially decayed stems of various sizes. It is illustrated in the large steles shown 

 in figs. 76-78, PI. X. The markings on the xylem disappear, while dark material is 

 deposited throughout the stele (fig. 76). This leads to a dark core representing 

 the xylem surrounded by a dark zone in the position of the phloem. A somewhat 

 similar condition is represented in fig. 77, where, however, the inner portion of the 

 phloem has broken down, leaving a clear space between a dark central mass and a 

 surrounding dark ring. In fig. 78, though decay is less advanced, the xylem (x-) 

 actually appears lighter in tint than the phloem (ph.), and has lost all its thickening, 

 while the zone of phloem appears to consist of elongated and very dark pointed 

 elements. 



This condition of preservation will be referred to further in the concluding remarks. 



